[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
@Stephane, did upstream ever accept your patch? -- You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. https://bugs.launchpad.net/bugs/595117 Title: qemu-nbd slow and missing writeback cache option -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
For the record, there's more on that bug at http://thread.gmane.org/gmane.linux.ubuntu.bugs.server/36923 -- You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. https://bugs.launchpad.net/bugs/595117 Title: qemu-nbd slow and missing writeback cache option -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
[Expired for qemu-kvm (Ubuntu) because there has been no activity for 60 days.] ** Changed in: qemu-kvm (Ubuntu) Status: Incomplete = Expired -- You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. https://bugs.launchpad.net/bugs/595117 Title: qemu-nbd slow and missing writeback cache option -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
Re: [Qemu-devel] [Bug 595117] Re: qemu-nbd slow and missing writeback cache option
2010-06-24 00:16:03 -, Jamie Lokier: Serge Hallyn wrote: The default of qemu-img (of using O_SYNC) is not very sensible because anyway, the client (the kernel) uses caches (write-back), (and qemu-nbd -d doesn't flush those by the way). So if for instance qemu-nbd is killed, regardless of whether qemu-nbd uses O_SYNC, O_DIRECT or not, the data in the image will not be consistent anyway, unless syncs are done by the client (like fsync on the nbd device or sync mount option), and with qemu-nbd's O_SYNC mode, those syncs will be extremely slow. Do the client syncs cause the nbd server to fsync or fdatasync the file? The clients syncs cause the data to be sent to the server. The server then writes it to disk and each write blocks until the data is written physically on disk with O_SYNC. It appears it is because by default the disk image it serves is open with O_SYNC. The --nocache option, unintuitively, makes matters a bit better because it causes the image to be open with O_DIRECT instead of O_SYNC. [...] --cache=off is the same as --nocache (that is use O_DIRECT), writethrough is using O_SYNC and is still the default so this patch doesn't change the functionality. writeback is none of those flags, so is the addition of this patch. The patch also does an fsync upon qemu-nbd -d to make sure data is flushed to the image before removing the nbd. I really wish qemu's options didn't give the false impression nocache does less caching than writethrough. O_DIRECT does caching in the disk controller/hardware, while O_SYNC hopefully does not, nowadays. [...] Note that I use the same none, writethrough, writeback as another utility shipped with qemu for consistency (see vl.c in the source), I don't mind about the words as long as the writeback functionality is available. Cheers, Stephane -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
** Changed in: qemu-kvm (Ubuntu) Status: Incomplete = Confirmed -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
** Changed in: qemu-kvm (Ubuntu) Status: Confirmed = Incomplete -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
Re: [Qemu-devel] [Bug 595117] Re: qemu-nbd slow and missing writeback cache option
Serge Hallyn wrote: The default of qemu-img (of using O_SYNC) is not very sensible because anyway, the client (the kernel) uses caches (write-back), (and qemu-nbd -d doesn't flush those by the way). So if for instance qemu-nbd is killed, regardless of whether qemu-nbd uses O_SYNC, O_DIRECT or not, the data in the image will not be consistent anyway, unless syncs are done by the client (like fsync on the nbd device or sync mount option), and with qemu-nbd's O_SYNC mode, those syncs will be extremely slow. Do the client syncs cause the nbd server to fsync or fdatasync the file? It appears it is because by default the disk image it serves is open with O_SYNC. The --nocache option, unintuitively, makes matters a bit better because it causes the image to be open with O_DIRECT instead of O_SYNC. [...] --cache=off is the same as --nocache (that is use O_DIRECT), writethrough is using O_SYNC and is still the default so this patch doesn't change the functionality. writeback is none of those flags, so is the addition of this patch. The patch also does an fsync upon qemu-nbd -d to make sure data is flushed to the image before removing the nbd. I really wish qemu's options didn't give the false impression nocache does less caching than writethrough. O_DIRECT does caching in the disk controller/hardware, while O_SYNC hopefully does not, nowadays. -- Jamie -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
Re: [Bug 595117] Re: qemu-nbd slow and missing writeback cache option
2010-06-16 20:36:00 -, Dustin Kirkland: [...] Could you please send that patch to the qemu-devel@ mailing list? Thanks! [...] Hi Dustin, it looks like qemu-devel is subscribed to bugs in there, so the bug report is on the list already. Note that I still consider it as a bug because: - slow performance for no good reason - --nocache option is misleading - no fsync on -d which to my mind is a bug. Cheers, Stephane -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
Re: [Bug 595117] Re: qemu-nbd slow and missing writeback cache option
Stephane- I understand your plight. However, according to the rules and policies of the QEMU project, you must submit the patch on the qemu-devel@ mailing list, in addition to (or instead of) in the bug tracker. It's not my project, not my policy. I'm just trying to make sure you get your patch in front of the right audience such that it can be discussed and accepted. -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
** Tags added: patch -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
** Patch added: qemu-nbd.diff http://launchpadlibrarian.net/50435882/qemu-nbd.diff -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
** Also affects: qemu Importance: Undecided Status: New ** Changed in: qemu-kvm (Ubuntu) Status: New = Confirmed -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
Noone has confirmed, but have passed along to upstream. If upstream takes this patch then we will likely pull it into our patchset. ** Changed in: qemu-kvm (Ubuntu) Status: Confirmed = Incomplete -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
Patches should go to qemu-devel, not bug reports. ** Changed in: qemu Status: New = Invalid -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
[Bug 595117] Re: qemu-nbd slow and missing writeback cache option
Stephane- Could you please send that patch to the qemu-devel@ mailing list? Thanks! -- qemu-nbd slow and missing writeback cache option https://bugs.launchpad.net/bugs/595117 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
