Re: [PATCH 0/2] rwsem: performance enhancements for systems withmany cores
From: Davidlohr Bueso
Date: Fri Jun 21 2013 - 20:00:37 EST
On Fri, 2013-06-21 at 16:51 -0700, Tim Chen wrote:
> In this patchset, we introduce two optimizations to read write semaphore.
> The first one reduces cache bouncing of the sem->count field
> by doing a pre-read of the sem->count and avoid cmpxchg if possible.
> The second patch introduces similar optimistic spining logic in
> the mutex code for the writer lock acquisition of rw-sem.
> Combining the two patches, in testing by Davidlohr Bueso on aim7 workloads
> on 8 socket 80 cores system, he saw improvements of
> alltests (+14.5%), custom (+17%), disk (+11%), high_systime
> (+5%), shared (+15%) and short (+4%), most of them after around 500
> users when i_mmap was implemented as rwsem.
> Feedbacks on the effectiveness of these tweaks on other workloads
> will be appreciated.
Tim, I was really hoping to send all this in one big bundle. I was doing
some further testing (enabling hyperthreading and some Oracle runs),
fortunately everything looks ok and we are getting actual improvements
on large boxes.
That said, how about I send you my i_mmap rwsem patchset for a v2 of
> Alex Shi (1):
> rwsem: check the lock before cpmxchg in down_write_trylock and
> Tim Chen (1):
> rwsem: do optimistic spinning for writer lock acquisition
> Makefile | 2 +-
> include/asm-generic/rwsem.h | 8 +-
> include/linux/rwsem.h | 3 +
> init/Kconfig | 9 +++
> kernel/rwsem.c | 29 +++++++-
> lib/rwsem.c | 169 ++++++++++++++++++++++++++++++++++++++-----
> 6 files changed, 195 insertions(+), 25 deletions(-)
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