Messages in this thread | | | Date | Thu, 3 Oct 2013 09:32:12 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v8 0/9] rwsem performance optimizations |
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* Tim Chen <tim.c.chen@linux.intel.com> wrote:
> For version 8 of the patchset, we included the patch from Waiman to > streamline wakeup operations and also optimize the MCS lock used in > rwsem and mutex.
I'd be feeling a lot easier about this patch series if you also had performance figures that show how mmap_sem is affected.
These:
> Tim got the following improvement for exim mail server > workload on 40 core system: > > Alex+Tim's patchset: +4.8% > Alex+Tim+Waiman's patchset: +5.3%
appear to be mostly related to the anon_vma->rwsem. But once that lock is changed to an rwlock_t, this measurement falls away.
Peter Zijlstra suggested the following testcase:
===============================> In fact, try something like this from userspace:
n-threads:
pthread_mutex_lock(&mutex); foo = mmap(); pthread_mutex_lock(&mutex);
/* work */
pthread_mutex_unlock(&mutex); munma(foo); pthread_mutex_unlock(&mutex);
vs
n-threads:
foo = mmap(); /* work */ munmap(foo);
I've had reports that the former was significantly faster than the latter. <===============================
this could be put into a standalone testcase, or you could add it as a new subcommand of 'perf bench', which already has some pthread code, see for example in tools/perf/bench/sched-messaging.c. Adding:
perf bench mm threads
or so would be a natural thing to have.
Thanks,
Ingo
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