| Message ID | 1535316795-21560-1-git-send-email-longman@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | xfs: Reduce spinlock contention in log space slowpath code | expand |
On Sun, Aug 26, 2018 at 04:53:12PM -0400, Waiman Long wrote: > v1->v2: > - For patch 1, remove wake_q_empty() & add task_in_wake_q(). > - Rewrite patch 2 after comments from Dave Chinner and break it down > to 2 separate patches. Now the original xfs logic was kept. The > patches just try to move the task wakeup calls to outside the > spinlock. > > While running the AIM7 microbenchmark on a small xfs filesystem, it > was found that there was a severe spinlock contention problem in the > current XFS log space reservation code. To alleviate the problem, the Again I'll ask: what is the performance when the log is made large enough that your benchmark is *not hammering the slow path*? i.e. does running "mkfs.xfs -l size=2000m ..." instead of using the default tiny log on your tiny test filesystem make the problem go away? Without that information, we have no idea what the slow path impact on peformance actually is, and whether it is worth persuing optimising slow path behaviour that very, very few production environments see lock contention in.... Cheers, Dave.
v1->v2: - For patch 1, remove wake_q_empty() & add task_in_wake_q(). - Rewrite patch 2 after comments from Dave Chinner and break it down to 2 separate patches. Now the original xfs logic was kept. The patches just try to move the task wakeup calls to outside the spinlock. While running the AIM7 microbenchmark on a small xfs filesystem, it was found that there was a severe spinlock contention problem in the current XFS log space reservation code. To alleviate the problem, the patches try to move as much task wakeup code to outside the spinlock using the wake_q mechanism so as to reduce the lock hold time as much as possible. Patch 1 exports the wake_up_q() and wake_q_add() functions and adds the task_in_wake_q() inline function. Patch 2 adds a new flag XLOG_TIC_WAKING to mark a task that is being waken up and skip the wake_up_process() if a previous wakeup has been issued. Patch 3 modifies the xlog_grant_head_wait() and xlog_grant_head_wake() functions to use wake_q for waking up tasks outside the lock critical section instead of calling wake_up_process() directly. The following table shows the performance improvement in the AIM7 fserver workload after applying patches 2 and 3: Patches Jobs/min % Change ------- -------- -------- - 91,486 - 2 192,666 +111% 2+3 285,221 +212% So the final patched kernel performed more than 3X better than the unpatched one. Waiman Long (3): sched/core: Export wake_q functions to kernel modules xfs: Prevent multiple wakeups of the same log space waiter xfs: Use wake_q for waking up log space waiters fs/xfs/xfs_linux.h | 1 + fs/xfs/xfs_log.c | 57 ++++++++++++++++++++++++++++++------ fs/xfs/xfs_log_priv.h | 1 + include/linux/sched/wake_q.h | 5 ++++ kernel/sched/core.c | 2 ++ 5 files changed, 57 insertions(+), 9 deletions(-)