Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
On 08/24/2017 10:04 AM, Oleksandr Andrushchenko wrote: Hello, On 08/24/2017 07:38 AM, Takashi Sakamoto wrote: On Aug 23 2017 23:51, Oleksandr Grytsov wrote: Hi, Thank you for detailed explanation. We understand that emulated interrupt on the frontend side is completely not acceptable and definitely we need to provide some feedback mechanism from Dom0 to DomU. In our case it is technically impossible to provide precise period interrupt (mostly because our backend is a user space application). The best we can implement it is provide number of frames (time, bytes etc.) consumed by real HW. This info will be outdated due to different delays but we can provide precise timestamps when this info was acquired. Stuffs of ALSA PCM in kernel land is an abstraction layer for actual hardware for data transmission. The stuffs get affects from a design of actual hardware. Furthermore, sound subsystems on the other operating systems such as Microsoft Windows are also designed with a consideration about actual hardware. When you design any interfaces as an abstraction for such software layer, it's better to understand actual hardware and design of low-level software layer somehow. Actually the 'sndif' has no good abstraction for actual hardware, therefore an idea to implement frontend driver as an ALSA driver is not reasonable at all. the reason for that is that you can use the same frontend driver for various DomUs without the need to write yet another HAL/application, e.g. if one of the DomUs has no PulseAudio (uses ALSA) and yet another DomU has PulseAudio, then using the same driver allows you to enable both out of the box with the same codebase. If we can imagine something else running on top of ALSA (say some other mixing software other than PulseAudio) then we will have to support that as well It's better to implement it as an application in the other software layer, e.g. sinks/sources of PulseAudio in DomU please see our reasoning above via Xenbus. This idea is nearer an original concept of Xen framework, I guess. But I don't know we can write any applications of Xenbus in user land of DomU or not. Anyway, it's not a good idea to have an ALSA driver for the present 'sndif', in my opinion. ok, so the main concern here is that we cannot properly synchronize Dom0-DomU. If we put this apart for a second are there any other concerns on having ALSA frontend driver? If not, can we have the driver with timer implementation upstreamed as experimental until we have some acceptable synchronization solution? This will allow broader audience to try and feel the solution and probably contribute? any thoughts on this? Regards Takashi Sakamoto Thank you very much for your time, Oleksandr Andrushchenko ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
Hello, On 08/24/2017 07:38 AM, Takashi Sakamoto wrote: On Aug 23 2017 23:51, Oleksandr Grytsov wrote: Hi, Thank you for detailed explanation. We understand that emulated interrupt on the frontend side is completely not acceptable and definitely we need to provide some feedback mechanism from Dom0 to DomU. In our case it is technically impossible to provide precise period interrupt (mostly because our backend is a user space application). The best we can implement it is provide number of frames (time, bytes etc.) consumed by real HW. This info will be outdated due to different delays but we can provide precise timestamps when this info was acquired. Stuffs of ALSA PCM in kernel land is an abstraction layer for actual hardware for data transmission. The stuffs get affects from a design of actual hardware. Furthermore, sound subsystems on the other operating systems such as Microsoft Windows are also designed with a consideration about actual hardware. When you design any interfaces as an abstraction for such software layer, it's better to understand actual hardware and design of low-level software layer somehow. Actually the 'sndif' has no good abstraction for actual hardware, therefore an idea to implement frontend driver as an ALSA driver is not reasonable at all. the reason for that is that you can use the same frontend driver for various DomUs without the need to write yet another HAL/application, e.g. if one of the DomUs has no PulseAudio (uses ALSA) and yet another DomU has PulseAudio, then using the same driver allows you to enable both out of the box with the same codebase. If we can imagine something else running on top of ALSA (say some other mixing software other than PulseAudio) then we will have to support that as well It's better to implement it as an application in the other software layer, e.g. sinks/sources of PulseAudio in DomU please see our reasoning above via Xenbus. This idea is nearer an original concept of Xen framework, I guess. But I don't know we can write any applications of Xenbus in user land of DomU or not. Anyway, it's not a good idea to have an ALSA driver for the present 'sndif', in my opinion. ok, so the main concern here is that we cannot properly synchronize Dom0-DomU. If we put this apart for a second are there any other concerns on having ALSA frontend driver? If not, can we have the driver with timer implementation upstreamed as experimental until we have some acceptable synchronization solution? This will allow broader audience to try and feel the solution and probably contribute? Regards Takashi Sakamoto Thank you very much for your time, Oleksandr Andrushchenko ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
On Aug 23 2017 23:51, Oleksandr Grytsov wrote: Hi, Thank you for detailed explanation. We understand that emulated interrupt on the frontend side is completely not acceptable and definitely we need to provide some feedback mechanism from Dom0 to DomU. In our case it is technically impossible to provide precise period interrupt (mostly because our backend is a user space application). The best we can implement it is provide number of frames (time, bytes etc.) consumed by real HW. This info will be outdated due to different delays but we can provide precise timestamps when this info was acquired. Stuffs of ALSA PCM in kernel land is an abstraction layer for actual hardware for data transmission. The stuffs get affects from a design of actual hardware. Furthermore, sound subsystems on the other operating systems such as Microsoft Windows are also designed with a consideration about actual hardware. When you design any interfaces as an abstraction for such software layer, it's better to understand actual hardware and design of low-level software layer somehow. Actually the 'sndif' has no good abstraction for actual hardware, therefore an idea to implement frontend driver as an ALSA driver is not reasonable at all. It's better to implement it as an application in the other software layer, e.g. sinks/sources of PulseAudio in DomU via Xenbus. This idea is nearer an original concept of Xen framework, I guess. But I don't know we can write any applications of Xenbus in user land of DomU or not. Anyway, it's not a good idea to have an ALSA driver for the present 'sndif', in my opinion. Regards Takashi Sakamoto ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
Hi, Thank you for detailed explanation. We understand that emulated interrupt on the frontend side is completely not acceptable and definitely we need to provide some feedback mechanism from Dom0 to DomU. In our case it is technically impossible to provide precise period interrupt (mostly because our backend is a user space application). The best we can implement it is provide number of frames (time, bytes etc.) consumed by real HW. This info will be outdated due to different delays but we can provide precise timestamps when this info was acquired. Would this info be useful to update the frontend driver state? If you have in mind any other solution we would appreciate. -- Best Regards, Oleksandr Grytsov. ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
Hi, On Aug 18 2017 16:23, Oleksandr Andrushchenko wrote: >> You mean that any alsa-lib or libpulse applications run on Dom0 as a >> backend driver for the frontend driver on DomU? >> > No, the sound backend [1] is a user-space application (ALSA/PulseAudio > client) > which runs as a Xen para-virtual backend in Dom0 and serves all the > frontends running in DomU(s). > Other ALSA/PulseAudio clients in Dom0 are also allowed to run at the > same time. > > [1] https://github.com/xen-troops/snd_be Actually, you did what I meant. Playback Capture delay DomU-ADomU-BDomU-C delay - - - | | | | | | (queueing) | App-A | | App-B | | App-C | (handling) | | | | | | | ^ | | (TSS) | | (TSS) | | (TSS) | | | | | | | | | | | ---^- ^ ^ | | ===|==|=| XenBus and| | ---|--| | mapped page frame | | Dom0 | v v v | | | |App-0 App-1 App-2 | | | | ^ ^ ^ | | | | |-> App-3<-| | | | | |(IPC) ^ (IPC) | | | | | v v | | | |==HW abstraction for TSS ==| | | | ^ ^ | | | ---|-|--- | | | |(TSS = Time Sharing System) | | v v | | Hardwares| v v | (presenting) physical part (sampling) I can easily imagine that several applications (App[0|1|2]) run in Dom0 as backend drivers of this context, to add several 'virtual' sound device for DomU, via Xenbus. The backend drivers can handle different hardware for the 'virtual' sound devices; e.g. it can be BSD socket applications. Of course, this is a sample based on my imagination. Actually, you assume that your application exclusively produces the 'virtual' sound cards, I guess. Anyway, it's not a point of this discussion. > In order to implement option 1) discussed (Interrupts to respond events from > actual hardware) we did number of experiments to find out if it can be > implemented in the way it satisfies the requirements with respect to latency, > interrupt number and use-cases. > > First of all the sound backend is a user-space application which uses either > ALSA or PulseAudio to play/capture audio depending on configuration. > Most of the use-cases we have are using PulseAudio as it allows to > implement more complex use cases then just plain ALSA. When assuming App-3 in the above diagram as PulseAudio, a combination of App-0/App-1/App-3 may correspond to the backend driver in your use-case. > We started to look at how can we get such an event so it can be used as > a period elapsed notification to the backend. > > In case of ALSA we used poll mechanism to wait for events from ALSA: > we configured SW params to have period event, but the problem here is that > it is notified not only when period elapses, but also when ALSA is ready to > consume more data. There is no mechanism to distinguish between these > two events (please correct us if there is one). Anyways, even if ALSA provides > period event to user-space (again, backend is a user-space application) > latency will consist of: time from kernel to user-space, user-space Dom0 to > frontend driver DomU. Both are variable and depend on many factors, > so the latency is not deterministic. > > (We were also thinking that we can implement a helper driver in Dom0 to have > a dedicated channel from ALSA to the backend to deliver period elapsed event, > so for instance, it can have some kind of a hook on snd_pcm_period_elapsed, > but it will not solve the use-case with PulseAudio discussed below. > Also it is unclear how to handle scenario when multiple DomU plays through > mixer with different frame rates, channels etc.). In design of ALSA PCM core, processes are awakened from poll wait by the other running tasks, which calculate available space on PCM buffer. This is done by a call of 'snd_pcm_hw_prw0()' in 'sound/core/pcm_lib.c' in kernel land. In this function, ALSA PCM core calls implementation of 'struct snd_pcm_ops.pointer()' in each driver and get current position of data transmission within buffer size, then 'hw_ptr' of PCM buffer is updated, then c
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
On 08/18/2017 10:17 AM, Takashi Sakamoto wrote: On Aug 18 2017 14:56, Oleksandr Andrushchenko wrote: Taking into account the fact that the backend we have is a user-space application running on top of ALSA/PulseAudio we cannot get HW pointers from actual hardware by any means (PulseAudio use-case is the most tough thing in equation) You mean that any alsa-lib or libpulse applications run on Dom0 as a backend driver for the frontend driver on DomU? No, the sound backend [1] is a user-space application (ALSA/PulseAudio client) which runs as a Xen para-virtual backend in Dom0 and serves all the frontends running in DomU(s). Other ALSA/PulseAudio clients in Dom0 are also allowed to run at the same time. Regards Takashi Sakamoto Thank you, Oleksandr [1] https://github.com/xen-troops/snd_be ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
On Aug 18 2017 14:56, Oleksandr Andrushchenko wrote: Taking into account the fact that the backend we have is a user-space application running on top of ALSA/PulseAudio we cannot get HW pointers from actual hardware by any means (PulseAudio use-case is the most tough thing in equation) You mean that any alsa-lib or libpulse applications run on Dom0 as a backend driver for the frontend driver on DomU? Regards Takashi Sakamoto ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
Hello, On 08/18/2017 08:43 AM, Takashi Sakamoto wrote: On Aug 17 2017 19:05, Oleksandr Grytsov wrote: So, from the above we think that period elapsed event derived in the described ways may not improve latency and will complicate the system. So, for that reason we are thinking of the option 2) (Positions of actual data transmission in any serial sound interfaces of actual hardwares.) Please declare the way to enable stuffs on DomU to get the positions from actual hardware. This is what we haven't investigated yet in detail as we were mostly focusing on period elapsed approach, so we can report our findings to the community. Taking into account the fact that the backend we have is a user-space application running on top of ALSA/PulseAudio we cannot get HW pointers from actual hardware by any means (PulseAudio use-case is the most tough thing in equation) At the moment we are seeking for any advise from more experienced developers in the field on possible ways to solve the problem of Dom0/DomU synchronization. Hope, together we can identify such a way that would be accepted by the community. If you have something on your mind could you please share your thoughts? Regards Takashi Sakamoto Thank you, Oleksandr Andrushchenko ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
On Aug 17 2017 19:05, Oleksandr Grytsov wrote: So, from the above we think that period elapsed event derived in the described ways may not improve latency and will complicate the system. So, for that reason we are thinking of the option 2) (Positions of actual data transmission in any serial sound interfaces of actual hardwares.) Please declare the way to enable stuffs on DomU to get the positions from actual hardware. Regards Takashi Sakamoto ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
On Thu, Aug 10, 2017 at 11:10 AM, Oleksandr Andrushchenko wrote: > Hi, > > thank you very much for valuable comments and your time! > > > On 08/10/2017 06:14 AM, Takashi Sakamoto wrote: >> >> Hi, >> >> On Aug 7 2017 21:22, Oleksandr Andrushchenko wrote: >>> >>> From: Oleksandr Andrushchenko >>> >>> This patch series adds support for Xen [1] para-virtualized >>> sound frontend driver. It implements the protocol from >>> include/xen/interface/io/sndif.h with the following limitations: >>> - mute/unmute is not supported >>> - get/set volume is not supported >>> Volume control is not supported for the reason that most of the >>> use-cases (at the moment) are based on scenarious where >>> unprivileged OS (e.g. Android, AGL etc) use software mixers. >>> >>> Both capture and playback are supported. >>> >>> Thank you, >>> Oleksandr >>> >>> Resending because of rebase onto [2] + added missing patch >>> >>> [1] https://xenproject.org/ >>> [2] >>> https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/log/?h=for-next >>> >>> Oleksandr Andrushchenko (12): >>>ALSA: vsnd: Introduce Xen para-virtualized sound frontend driver >>>ALSA: vsnd: Implement driver's probe/remove >>>ALSA: vsnd: Implement Xen bus state handling >>>ALSA: vsnd: Read sound driver configuration from Xen store >>>ALSA: vsnd: Implement Xen event channel handling >>>ALSA: vsnd: Implement handling of shared buffers >>>ALSA: vsnd: Introduce ALSA virtual sound driver >>>ALSA: vsnd: Initialize virtul sound card >>>ALSA: vsnd: Add timer for period interrupt emulation >>>ALSA: vsnd: Implement ALSA PCM operations >>>ALSA: vsnd: Implement communication with backend >>>ALSA: vsnd: Introduce Kconfig option to enable Xen PV sound >>> >>> sound/drivers/Kconfig | 12 + >>> sound/drivers/Makefile|2 + >>> sound/drivers/xen-front.c | 2107 >>> + >>> 3 files changed, 2121 insertions(+) >>> create mode 100644 sound/drivers/xen-front.c >> >> >> For this patchset, I have the same concern which Clemens Ladisch >> denoted[1]. If I can understand your explanation about queueing between >> Dom0/DomU stuffs, the concern can be described in short words; this >> driver works without any synchronization to data transmission by actual >> sound hardwares. >> > Yes, both your concerns and understanding are correct >> >> In design of ALSA PCM core, drivers are expected to synchronize to >> actual hardwares for semi-realtime data transmission. The >> synchronization is done by two points: >> 1) Interrupts to respond events from actual hardwares. >> 2) Positions of actual data transmission in any serial sound interfaces >>of actual hardwares. >> >> These two points comes from typical designs of actual hardwares, thus >> they doesn't come from unfair, unreasonable, intrusive demands from >> software side. >> > This clear, thank you >> >> In design of typical stuffs on para-virtualization, Dom0 stuffs are hard >> to give enough abstraction of sound hardwares in these two points for >> DomU stuffs. Especially, it cannot abstract point 2) at all because the >> value of position should be accurate against actual time frame, while >> there's an overhead for DomU stuffs to read it. When DomU stuffs handles >> the value, the value is enough past due to context switches between >> Dom0/DomU. Therefore, this driver must rely on point 1) to synchronize >> to actual sound hardwares. In order to implement option 1) discussed (Interrupts to respond events from actual hardwares) we did number of experiments to find out if it can be implemented in the way it satisfies the requirements with respect to latency, interrupt number and use-cases. First of all the sound backend is a user-space application which uses either ALSA or PulseAudio to play/capture audio depending on configuration. Most of the use-cases we have are using PulseAudio as it allows to implement more complex use cases then just plain ALSA. We started to look at how can we get such an event so it can be used as a period elapsed notification to the backend. In case of ALSA we used poll mechanism to wait for events from ALSA: we configured SW params to have period event, but the problem here is that it is notified not only when period elapses, but also when ALSA is ready to consume more data. There is no mechanism to distinguish between these two events (please correct us if there is one). Anyways, even if ALSA provides period event to user-space (again, backend is a user-space application) latency will consist of: time from kernel to user-space, user-space Dom0 to frontend driver DomU. Both are variable and depend on many factors, so the latency is not deterministic. (We were also thinking that we can implement a helper driver in Dom0 to have a dedicated channel from ALSA to the backend to deliver period elapsed event, so for instance, it can have some kind of a hook on snd_pcm_period_elapsed, but it will not
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
Hi, thank you very much for valuable comments and your time! On 08/10/2017 06:14 AM, Takashi Sakamoto wrote: Hi, On Aug 7 2017 21:22, Oleksandr Andrushchenko wrote: From: Oleksandr Andrushchenko This patch series adds support for Xen [1] para-virtualized sound frontend driver. It implements the protocol from include/xen/interface/io/sndif.h with the following limitations: - mute/unmute is not supported - get/set volume is not supported Volume control is not supported for the reason that most of the use-cases (at the moment) are based on scenarious where unprivileged OS (e.g. Android, AGL etc) use software mixers. Both capture and playback are supported. Thank you, Oleksandr Resending because of rebase onto [2] + added missing patch [1] https://xenproject.org/ [2] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/log/?h=for-next Oleksandr Andrushchenko (12): ALSA: vsnd: Introduce Xen para-virtualized sound frontend driver ALSA: vsnd: Implement driver's probe/remove ALSA: vsnd: Implement Xen bus state handling ALSA: vsnd: Read sound driver configuration from Xen store ALSA: vsnd: Implement Xen event channel handling ALSA: vsnd: Implement handling of shared buffers ALSA: vsnd: Introduce ALSA virtual sound driver ALSA: vsnd: Initialize virtul sound card ALSA: vsnd: Add timer for period interrupt emulation ALSA: vsnd: Implement ALSA PCM operations ALSA: vsnd: Implement communication with backend ALSA: vsnd: Introduce Kconfig option to enable Xen PV sound sound/drivers/Kconfig | 12 + sound/drivers/Makefile|2 + sound/drivers/xen-front.c | 2107 + 3 files changed, 2121 insertions(+) create mode 100644 sound/drivers/xen-front.c For this patchset, I have the same concern which Clemens Ladisch denoted[1]. If I can understand your explanation about queueing between Dom0/DomU stuffs, the concern can be described in short words; this driver works without any synchronization to data transmission by actual sound hardwares. Yes, both your concerns and understanding are correct In design of ALSA PCM core, drivers are expected to synchronize to actual hardwares for semi-realtime data transmission. The synchronization is done by two points: 1) Interrupts to respond events from actual hardwares. 2) Positions of actual data transmission in any serial sound interfaces of actual hardwares. These two points comes from typical designs of actual hardwares, thus they doesn't come from unfair, unreasonable, intrusive demands from software side. This clear, thank you In design of typical stuffs on para-virtualization, Dom0 stuffs are hard to give enough abstraction of sound hardwares in these two points for DomU stuffs. Especially, it cannot abstract point 2) at all because the value of position should be accurate against actual time frame, while there's an overhead for DomU stuffs to read it. When DomU stuffs handles the value, the value is enough past due to context switches between Dom0/DomU. Therefore, this driver must rely on point 1) to synchronize to actual sound hardwares. Which will also introduce some latency too: time needed to deliver and handle interrupt from Dom0 to DomU Typically, drivers configure hardwares to generate interrupts per period of PCM buffer. This means that this driver should notify to Dom0 about the value of period size requested by applications. In 'include/xen/interface/io/sndif.h', there's no functionalities I described the above: 1. notifications from DomU to Dom0 about the size of period for interrupts from actual hardwares. Or no way from Dom0 to DomU about the configured size of the period. Ok, then on "open" command I will pass from DomU to Dom0 an additional parameter, period size. Then Dom0 will respond with actual period size for DomU to use. So, this way period size will be negotiated. Does the above look ok to you? 2. notifications of the interrupts from actual hardwares to DomU. Ok, I will introduce an event from Dom0 to DomU to signal period elapsed. Taking into account the fact that period size may be as small as, say, 1ms, do you think we can/need to mangle period size in 1) on Dom0 side to be reasonable, so we do not flood with interrupts/events from Dom0 to DomU? Do you see any "formula" to determine that reasonable/acceptable period limit, so both Dom0 and DomU are happy? For the reasons, your driver used kernel's timer interface to generate 'pseudo' interrupts for the purpose. However, it depends on Dom0's abstraction different from sound hardwares and Linux kernel's abstraction for timer functionality. In this case, gap between 'actual' interrupts from hardware and the 'pseudo' interrupts from a combination of several components brings unexpected result on several situations. You are right I think this is defects of 'sndif' interface in Xen side. I think it better for you to work in Xen community to improve the above i
Re: [Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
Hi, On Aug 7 2017 21:22, Oleksandr Andrushchenko wrote: From: Oleksandr Andrushchenko This patch series adds support for Xen [1] para-virtualized sound frontend driver. It implements the protocol from include/xen/interface/io/sndif.h with the following limitations: - mute/unmute is not supported - get/set volume is not supported Volume control is not supported for the reason that most of the use-cases (at the moment) are based on scenarious where unprivileged OS (e.g. Android, AGL etc) use software mixers. Both capture and playback are supported. Thank you, Oleksandr Resending because of rebase onto [2] + added missing patch [1] https://xenproject.org/ [2] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/log/?h=for-next Oleksandr Andrushchenko (12): ALSA: vsnd: Introduce Xen para-virtualized sound frontend driver ALSA: vsnd: Implement driver's probe/remove ALSA: vsnd: Implement Xen bus state handling ALSA: vsnd: Read sound driver configuration from Xen store ALSA: vsnd: Implement Xen event channel handling ALSA: vsnd: Implement handling of shared buffers ALSA: vsnd: Introduce ALSA virtual sound driver ALSA: vsnd: Initialize virtul sound card ALSA: vsnd: Add timer for period interrupt emulation ALSA: vsnd: Implement ALSA PCM operations ALSA: vsnd: Implement communication with backend ALSA: vsnd: Introduce Kconfig option to enable Xen PV sound sound/drivers/Kconfig | 12 + sound/drivers/Makefile|2 + sound/drivers/xen-front.c | 2107 + 3 files changed, 2121 insertions(+) create mode 100644 sound/drivers/xen-front.c For this patchset, I have the same concern which Clemens Ladisch denoted[1]. If I can understand your explanation about queueing between Dom0/DomU stuffs, the concern can be described in short words; this driver works without any synchronization to data transmission by actual sound hardwares. In design of ALSA PCM core, drivers are expected to synchronize to actual hardwares for semi-realtime data transmission. The synchronization is done by two points: 1) Interrupts to respond events from actual hardwares. 2) Positions of actual data transmission in any serial sound interfaces of actual hardwares. These two points comes from typical designs of actual hardwares, thus they doesn't come from unfair, unreasonable, intrusive demands from software side. In design of typical stuffs on para-virtualization, Dom0 stuffs are hard to give enough abstraction of sound hardwares in these two points for DomU stuffs. Especially, it cannot abstract point 2) at all because the value of position should be accurate against actual time frame, while there's an overhead for DomU stuffs to read it. When DomU stuffs handles the value, the value is enough past due to context switches between Dom0/DomU. Therefore, this driver must rely on point 1) to synchronize to actual sound hardwares. Typically, drivers configure hardwares to generate interrupts per period of PCM buffer. This means that this driver should notify to Dom0 about the value of period size requested by applications. In 'include/xen/interface/io/sndif.h', there's no functionalities I described the above: 1. notifications from DomU to Dom0 about the size of period for interrupts from actual hardwares. Or no way from Dom0 to DomU about the configured size of the period. 2. notifications of the interrupts from actual hardwares to DomU. For the reasons, your driver used kernel's timer interface to generate 'pseudo' interrupts for the purpose. However, it depends on Dom0's abstraction different from sound hardwares and Linux kernel's abstraction for timer functionality. In this case, gap between 'actual' interrupts from hardware and the 'pseudo' interrupts from a combination of several components brings unexpected result on several situations. I think this is defects of 'sndif' interface in Xen side. I think it better for you to work in Xen community to improve the above interface at first, then work for Linux stuffs. Additionally, in next time, please remind of several points below: * When a first patch adds an initial code for drivers, it should include entries for Makefile and Kconfig, so that the driver can be built even if it's still in an initial shape. Each patch should be self-contained and should be in a shape so that developers easily run bisecting. In other words, your first patch[2] includes modification for Makefile and Kconfig in your last patch[3]. * When any read-only symbols is added, it should have 'const' qualifier so that the symbol places to .rodata section of ELF binaries. For example, in your code, 'alsa_sndif_formats' is such an symbol. In recent Linux development, some developers work for constifying such symbols. Please remind of their continuous works in upstream[4]. * You can split your driver to several files. In 'include/xen/interface/io/sndif.h', Dom0 pro
[Xen-devel] [PATCH RESEND1 00/12] ALSA: vsnd: Add Xen para-virtualized frontend driver
From: Oleksandr Andrushchenko This patch series adds support for Xen [1] para-virtualized sound frontend driver. It implements the protocol from include/xen/interface/io/sndif.h with the following limitations: - mute/unmute is not supported - get/set volume is not supported Volume control is not supported for the reason that most of the use-cases (at the moment) are based on scenarious where unprivileged OS (e.g. Android, AGL etc) use software mixers. Both capture and playback are supported. Thank you, Oleksandr Resending because of rebase onto [2] + added missing patch [1] https://xenproject.org/ [2] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/log/?h=for-next Oleksandr Andrushchenko (12): ALSA: vsnd: Introduce Xen para-virtualized sound frontend driver ALSA: vsnd: Implement driver's probe/remove ALSA: vsnd: Implement Xen bus state handling ALSA: vsnd: Read sound driver configuration from Xen store ALSA: vsnd: Implement Xen event channel handling ALSA: vsnd: Implement handling of shared buffers ALSA: vsnd: Introduce ALSA virtual sound driver ALSA: vsnd: Initialize virtul sound card ALSA: vsnd: Add timer for period interrupt emulation ALSA: vsnd: Implement ALSA PCM operations ALSA: vsnd: Implement communication with backend ALSA: vsnd: Introduce Kconfig option to enable Xen PV sound sound/drivers/Kconfig | 12 + sound/drivers/Makefile|2 + sound/drivers/xen-front.c | 2107 + 3 files changed, 2121 insertions(+) create mode 100644 sound/drivers/xen-front.c -- 2.7.4 ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel