On Tue, Jan 23, 2018 at 07:25:05PM +0200, Avi Kivity wrote: > > > On 01/23/2018 06:31 PM, Brian Foster wrote: > > On Tue, Jan 23, 2018 at 06:10:51PM +0200, Avi Kivity wrote: > > > I'm seeing the following lock contention in io_submit() (unfortunately, > > > older kernel again) > > > > > > > > > 0xffffffff816ab231 : __schedule+0x531/0x9b0 [kernel] > > > 0xffffffff816ab6d9 : schedule+0x29/0x70 [kernel] > > > 0xffffffff816acfc5 : rwsem_down_write_failed+0x225/0x3a0 [kernel] > > > 0xffffffff81333ca7 : call_rwsem_down_write_failed+0x17/0x30 [kernel] > > > 0xffff8819bc3f3bf8 : 0xffff8819bc3f3bf8 > > > 0xffffffff816aa8bd : down_write+0x2d/0x3d [kernel] > > > 0xffffffffc00ca1d1 : xfs_ilock+0xc1/0x120 [xfs] > > > 0xffffffffc00c7c8d : xfs_vn_update_time+0xcd/0x150 [xfs] > > > 0xffffffff8121eda5 : update_time+0x25/0xd0 [kernel] > > > 0xffffffff8121eef0 : file_update_time+0xa0/0xf0 [kernel] > > > 0xffffffffc00be3a5 : xfs_file_aio_write_checks+0x185/0x1f0 [xfs] > > > 0xffffffffc00be6c9 : xfs_file_dio_aio_write+0xd9/0x390 [xfs] > > > 0xffffffffc00bed42 : xfs_file_aio_write+0x102/0x1b0 [xfs] > > > 0xffffffffc00bec40 : xfs_file_aio_write+0x0/0x1b0 [xfs] > > > 0xffffffff81255ff8 : do_io_submit+0x3b8/0x870 [kernel] > > > > > > > > > There is only one thread issuing those writes, and nobody is reading the > > > file. Who could possibly be contending on this lock? > > > > > That looks like XFS_ILOCK_EXCL, which is a low level lock and thus not > > necessarily restricted to user-driven operations. One possible example > > of a background user is xfsaild, which acquires XFS_ILOCK_SHARED (and > > thus locks out exclusive waiters) via xfs_inode_item_push() in order to > > flush the dirty inode to disk (i.e., metadata writeback). > > > > I'm not exactly sure that's what is going on in your particular case, > > but I think tracepoints are your friend here. ;) E.g., 'trace-cmd record > > -e xfs:xfs_ilock' for the ilock, perhaps others for more context if > > necessary.. > > Here's what trace-cmd reported. I'm tracing xfs_ilock, xfs_iunlock, and > sched_switch: > > syscall-14-12006 [007] 108264.972883: xfs_ilock: dev 9:0 ino > 0x10008c9a flags ILOCK_SHARED caller xfs_file_fsync > <snip> > reactor-14-11979 [007] 108264.973292: xfs_iunlock: dev 9:0 ino > 0xa04d64c1 flags IOLOCK_SHARED caller xfs_file_dio_aio_read > reactor-14-11979 [007] 108264.973293: xfs_ilock: dev 9:0 ino > 0x10008c9a flags IOLOCK_SHARED caller xfs_file_dio_aio_write > reactor-14-11979 [007] 108264.973296: xfs_ilock: dev 9:0 ino > 0x10008c9a flags ILOCK_EXCL caller xfs_vn_update_time > reactor-14-11979 [007] 108264.973300: sched_switch: reactor-14:11979 > [120] D ==> kworker/7:1H:1350 [100] > <snip> > syscall-14-12006 [007] 108265.015795: xfs_iunlock: dev 9:0 ino > 0x10008c9a flags ILOCK_SHARED caller xfs_file_fsync > > > Is IOLOCK_SHARED mutually exclusive with ILOCK_EXCL? I'm guessing not. > Nope, they are separate locks. Brian > > Looks like fsync clashed with io_submit() here, which wasn't supposed to > happen in my code, they ought to be mutually exclusive. > > > > > I'm seeing 200ms stalls, so my guess is a log flush is involved. > > > > > > > > > Is this lock contention covered by RWF_NOWAIT? > > > > > I don't think so. It looked to me that RWF_NOWAIT basically just skips > > allocations.. > > > > Brian > > > > > -- > > > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
