Messages in this thread | | | Date | Thu, 31 Jan 2013 20:23:54 +0800 | From | Yuanhan Liu <> | Subject | Re: [PATCH] rwsem-spinlock: let rwsem write lock stealable |
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On Thu, Jan 31, 2013 at 11:45:41AM +0100, Ingo Molnar wrote: > > * Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote: > > > > > output with this patch: > > > > ----------------------- > > > > cpu 00: 0 0 ... 1 1 2 1 1 1 2 1 1 1 .... 1 3 > > > > cpu 01: 0 0 ... 1 1 1 1 1 1 2 1 1 1 .... 1 3 > > > > cpu 02: 0 0 ... 2 2 3 2 0 2 1 2 1 1 .... 1 1 > > > > cpu 03: 0 0 ... 2 2 3 2 1 2 1 2 1 1 .... 1 1 > > > > cpu 04: 0 1 ... 2 0 0 1 0 1 3 1 1 1 .... 1 1 > > > > cpu 05: 0 1 ... 2 0 1 1 0 1 2 1 1 1 .... 1 1 > > > > cpu 06: 0 0 ... 2 1 1 2 0 1 2 1 1 1 .... 2 1 > > > > cpu 07: 0 0 ... 2 1 1 2 0 1 2 1 1 1 .... 2 1 > > > > cpu 08: 0 0 ... 1 1 1 1 1 1 1 1 1 1 .... 0 0 > > > > cpu 09: 0 0 ... 1 1 1 1 1 1 1 1 1 1 .... 0 0 > > > > cpu 10: 0 0 ... 1 1 1 0 0 1 1 1 1 1 .... 0 0 > > > > cpu 11: 0 0 ... 1 1 1 0 0 1 1 1 1 2 .... 1 0 > > > > cpu 12: 0 0 ... 1 1 1 0 1 1 0 0 0 1 .... 2 1 > > > > cpu 13: 0 0 ... 1 1 1 0 1 1 1 0 1 2 .... 2 0 > > > > cpu 14: 0 0 ... 2 0 0 0 0 1 1 1 1 1 .... 2 2 > > > > cpu 15: 0 0 ... 2 0 0 1 0 1 1 1 1 1 .... 2 2 > > > > ------------------------------------------------------------------------ > > > > Where you can see that CPU is much busier with this patch. > > > > > > That looks really good - quite similar to how it behaved > > > with mutexes, right? > > > > Yes :) > > > > And the result is almost same with mutex lock when MUTEX_SPIN_ON_OWNER > > is disabled, and that's the reason you will see massive processes(about > > 100) queued on each CPU in my last report: > > https://lkml.org/lkml/2013/1/29/84 > > Just curious: how does MUTEX_SPIN_ON_OWNER versus > !MUTEX_SPIN_ON_OWNER compare, for this particular, > massively-contended anon-vma locks benchmark?
In above testcase, MUTEX_SPIN_ON_OWNER is slightly doing better job(like 3% ~ 4%) than !MUTEX_SPIN_ON_OWNER.
> > > > Does this recover most of the performance regression? > > > > Yes, there is only a 10% gap here then. I guess that's because
Sorry, to be accurate, it's about 14% gap; when MUTEX_SPIN_ON_OWNER is enabled.
> > I used the general rwsem lock > > implementation(lib/rwsem-spinlock.c), but not the XADD > > one(lib/rwsem.c). I guess the gap may be a little smaller if > > we do the same thing to lib/rwsem.c. > > Is part of the gap due to MUTEX_SPIN_ON_OWNER perhaps?
Nope, !MUTEX_SPIN_ON_OWNER does introduce a little performance drop just as above stated.
So, to make it clear, here is the list:
lock case performance drop compared to mutex lock ---------------------------------------------------------------------------- mutex lock w/o MUTEX_SPIN_ON_OWNER 3.x% rwsem-spinlock with write stealing 14.x% rwsem-spinlock >100%
> > I'm surprised that rwsem-spinlock versus rwsem.c would show a > 10% performance difference -
Yes, it may not. And there is only about 0.9% performance difference in above test between rwsem-spinlock and XADD rwsem. The difference maybe enlarged when both has write lock stealing enabled, which will be known only after we do same thing to lib/rwsem.c.
Thanks.
--yliu
> assuming you have lock > debugging/tracing disabled in the .config. > > ( Once the performance regression is fixed, another thing to > check would be to reduce anon-vma lock contention. ) > > Thanks, > > Ingo
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