Re: [systemd-devel] [PATCH v3 2/3] cxgb4: use module_long_probe_init()
On Fri, Aug 15, 2014 at 02:14:58AM +0200, Luis R. Rodriguez wrote: This driver also uses module_pci_driver() so a module_long_probe_driver() and respective module_long_probe_pci_driver() would need to be considered if but easily implemented (sent to Alex to test). No, don't create bus-only versions of the long probe function, just unwrap the module_pci_driver() logic and use the module_long_probe() call, we want it to be obvious that something is odd here and needs to be fixed someday. thanks, greg k-h ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] [PATCH v3 2/3] cxgb4: use module_long_probe_init()
On Thu, Aug 14, 2014 at 09:42:49AM -0700, Casey Leedom wrote: On 08/13/2014 04:33 PM, Anish Bhatt wrote: Adding Casey who's actually incharge of this code and missing from the CC list Thanks Anish! As I mentioned to Anish, there are fundamentally two problems here in the time being consumed by the cxgb4 PCI probe() function: 1. When various firmware files aren't present, request_firmware() can take a very long time. This is easily solved by using request_firmware_direct() and I certainly have no objection to that. I sent a patch for this a while ago, since there is no objection if you'd like to apply the patch: http://patchwork.ozlabs.org/patch/363756/ Apart from that you also want to use asynch firmware loading but to use that properly (I also had sent some basic initial patches for asynch firmware loading but without moving out other logic yet) you want to also let driver initalization complete asynchronously later. 2. When there are multiple adapters present in a system which need firmware downloaded, each one individually may not take a ton of time but together they can exceed simple Module Load Timeouts. There's not a simple answer here. I had originally recommended to write your own platform driver for this and have each port probe but Greg has provided the last advice for this on the patch I sent to add deferred probe support from init, his recommendation was for you to write your own bus code for the driver: http://www.spinics.net/lists/linux-scsi/msg76695.html Part of the problem here is that it's a Module Load Timeout instead of a per-device Probe Timeout. Seems like you can fix this with a bus driver. Part of the problem is that the current architecture has Device Probe happening out of the Module Initialization when we call pci_register_driver() with our PCI Device ID Table. Running the Device Probes asynchronously has been discussed but that has the problem that it's then impossible to return the Device Probe Status. This is a problem for Driver Fallback and, if the probe fails, we're not supposed to call the Device Remove function. To make this work, the synchronous/asynchronous boundary would really need to be up in the PCI Infrastructure layer so the Device Probe status could be captured in the normal logic. This would be a moderately large change there ... Some maintainers consider most of the work to get what you need done simple, I've tried to explain it ain't so, so glad you provided a bit of details here. To be clear its not just about asynch firmware loading, you need a bit more work. Can you evaluate using a bus driver? Deferring the Device Initialization till the first ifup has also been discussed and is certainly possible, though a moderately large architectural change to every driver which needs it. It also has the unfortunate effect of introducing random large delays directly on user commands. From a User Experience perspective I would tend to want such large delays in the Device Probe You should just use asynch firmware loading there and only once your driver is done loading firmware start exposing the device(s) as you see fit with your bus driver. . But that's something that really deserves a real User Interaction study rather than throwing a dart. On the whole, I think that introducing these Module Load Timeouts hasn't been well thought out with respect to the repercussions and I'd be more inclined to back that out till a well thought out design is developed. But I'm here for the discussion. The way that the 30 second timeout was introduced as a new driver initialization requirement was certainly not ideal specially since the respective systemd patch that intended to trigger the SIGKILL on kmod module loading only took effect once kernel commit 786235ee went in about a year later, and since the original systemd commit was only addressing asynchronous firmware loading as a possible issue that drivers may need to fix. The cxgb4 driver is a good example that needs quite a bit of more work. Regardless systemd folks are right -- but again, having this be introduced as a new requirement that otherwise simply kills drivers seems a bit too aggressive specially if its killing boot on some systems due to delays on storage drivers. What's done is done -- and we need to move on. We already reviewed twice now reverting 786235ee and that won't happen, as a compromise we're looking for an easy agreeable general driver work around that would both circumvent the issue and let us easily grep for broken drivers. The deferred probe trick was the first approach and this series addresses the more agreeable solution. This 2 line patch then is what we are looking as work around until your driver gets properly fixed. Apart from these kernel changes there are systemd changes we've looked at modifying, Hannes' patch 9719859c07a, now merged upstream on systemd lets you override the
Re: [systemd-devel] [PATCH v3 2/3] cxgb4: use module_long_probe_init()
On Thu, Aug 14, 2014 at 09:53:21PM +0200, Luis R. Rodriguez wrote: On Thu, Aug 14, 2014 at 09:42:49AM -0700, Casey Leedom wrote: Part of the problem is that the current architecture has Device Probe happening out of the Module Initialization when we call pci_register_driver() with our PCI Device ID Table. Running the Device Probes asynchronously has been discussed but that has the problem that it's then impossible to return the Device Probe Status. This is a problem for Driver Fallback and, if the probe fails, we're not supposed to call the Device Remove function. To make this work, the synchronous/asynchronous boundary would really need to be up in the PCI Infrastructure layer so the Device Probe status could be captured in the normal logic. This would be a moderately large change there ... Some maintainers consider most of the work to get what you need done simple, I've tried to explain it ain't so, so glad you provided a bit of details here. To be clear its not just about asynch firmware loading, you need a bit more work. Can you evaluate using a bus driver? -- snip -- On the whole, I think that introducing these Module Load Timeouts hasn't been well thought out with respect to the repercussions and I'd be more inclined to back that out till a well thought out design is developed. But I'm here for the discussion. The way that the 30 second timeout was introduced as a new driver initialization requirement was certainly not ideal specially since the respective systemd patch that intended to trigger the SIGKILL on kmod module loading only took effect once kernel commit 786235ee went in about a year later, and since the original systemd commit was only addressing asynchronous firmware loading as a possible issue that drivers may need to fix. The cxgb4 driver is a good example that needs quite a bit of more work. Regardless systemd folks are right -- but again, having this be introduced as a new requirement that otherwise simply kills drivers seems a bit too aggressive specially if its killing boot on some systems due to delays on storage drivers. What's done is done -- and we need to move on. We already reviewed twice now reverting 786235ee and that won't happen, as a compromise we're looking for an easy agreeable general driver work around that would both circumvent the issue and let us easily grep for broken drivers. The deferred probe trick was the first approach and this series addresses the more agreeable solution. This 2 line patch then is what we are looking as work around until your driver gets properly fixed. Apart from these kernel changes there are systemd changes we've looked at modifying, Hannes' patch 9719859c07a, now merged upstream on systemd lets you override the timeout value through the kernel command line. This will only help for all systems if you use a high enough large timeout value, or on a case by case basis for each system. I recently proposed replacing a kill for a warn only for udev kmod built in commands, that's unacceptable for systemd's architecture though so the last thing I proposed instead to use *for now* is a multiplier for each different type of udev built-in command and for kmod we'd use a high enough value, the timeout therefore would be really large for module loading for now, but we'd still want to collect logs of drivers taking long to probe. That's still being discussed [0] but my hope is that with this series and that other systemd discussion we'll have covered both areas affected and have a good strategy to move forward with this new driver requirement. [0] http://comments.gmane.org/gmane.comp.sysutils.systemd.devel/21689 Here's another affected driver: https://bugzilla.kernel.org/show_bug.cgi?id=59581 pata_marvell, and using the work around in this series should work, just as the deferred probe work around. Alexander however notes that the pata_marvell driver is just a simple wrapper and other devices can act the same way. This can surely be fixed perhaps in libata but its an example of an old driver and folks not being around to care much over drivers which are affected. This driver also uses module_pci_driver() so a module_long_probe_driver() and respective module_long_probe_pci_driver() would need to be considered if but easily implemented (sent to Alex to test). Luis ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
