Excerpts from Tejun Heo's message of 2011-03-21 12:59:55 -0400:
> Hello,
>
> Here are the results with voluntary preemption. I've moved to a
> beefier machine for testing. It's dual Opteron 2347, so dual socket,
> eight core. The memory is limited to 1GiB to force IOs and the disk
> is the same OCZ Vertex 60gig SSD. /proc/stat is captured before and
> after "dbench 50".
>
> I ran the following four setups.
>
> DFL The current custom locking implementation.
> SIMPLE Simple mutex conversion. The first patch in this thread.
> SPIN SIMPLE + mutex_tryspin(). The second patch in this thread.
> SPIN2 SPIN + mutex_tryspin() in btrfs_tree_lock(). Patch below.
>
> SPIN2 should alleviate the voluntary preemption by might_sleep() in
> mutex_lock().
>
> USER SYSTEM SIRQ CXTSW THROUGHPUT
> DFL 49427 458210 1433 7683488 642.947
> SIMPLE 52836 471398 1427 3055384 705.369
> SPIN 52267 473115 1467 3005603 705.369
> SPIN2 52063 470453 1446 3092091 701.826
>
> I'm running DFL again just in case but SIMPLE or SPIN seems to be a
> much better choice.
Very interesting. Ok, I'll definitely rerun my benchmarks as well. I
used dbench extensively during the initial tuning, but you're forcing
the memory low in order to force IO.
This case doesn't really hammer on the locks, it hammers on the
transition from spinning to blocking. We want also want to compare
dbench entirely in ram, which will hammer on the spinning portion.
-chris
>
> Thanks.
>
> NOT-Signed-off-by: Tejun Heo <t...@kernel.org>
> ---
> fs/btrfs/locking.h | 2 ++
> 1 file changed, 2 insertions(+)
>
> Index: work/fs/btrfs/locking.h
> ===================================================================
> --- work.orig/fs/btrfs/locking.h
> +++ work/fs/btrfs/locking.h
> @@ -28,6 +28,8 @@ static inline bool btrfs_try_spin_lock(s
>
> static inline void btrfs_tree_lock(struct extent_buffer *eb)
> {
> + if (mutex_tryspin(&eb->lock))
> + return;
> mutex_lock(&eb->lock);
> }
>
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