Re: [PATCH 0/2] rwsem: performance enhancements for systems with many cores

From: Michel Lespinasse
Date: Fri Jun 21 2013 - 20:25:22 EST

On Fri, Jun 21, 2013 at 5:00 PM, Davidlohr Bueso <davidlohr.bueso@xxxxxx> wrote:
> 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
> this patchset?

I'm a bit confused about the state of these patchsets - it looks like
I'm only copied into half of the conversations. Should I wait for a v2
here, or should I hunt down for Alex's version of things, or... ?

Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at