From: Ingo Molnar <mingo@kernel.org>
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Cc: Huang Ying <ying.huang@intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
David Howells <dhowells@redhat.com>,
linux-kernel@vger.kernel.org, lkp@linux.intel.com
Subject: Re: aim7 performance regression by commit 5a50508 report from LKP
Date: Tue, 29 Jan 2013 10:12:45 +0100 [thread overview]
Message-ID: <20130129091245.GB5775@gmail.com> (raw)
In-Reply-To: <20130129090620.GT12678@yliu-dev.sh.intel.com>
* Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:
> On Tue, Jan 29, 2013 at 09:44:00AM +0100, Ingo Molnar wrote:
> >
> > * Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:
> >
> > > [...]
> >
> > Very nice measurements and analysis, thanks!
> >
> > > As stated above, anybody can have a chance to own the lock in
> > > mutex once somebody release the lock. Well, there is only one
> > > to own the lock in rwsem write lock, and the one is known
> > > already: the one in the head of wait list. That would result
> > > to more contention in rwsem write lock case, especially if the
> > > one _will_ own the lock is not running now.
> >
> > I think we should allow lock-steal between rwsem writers - that
> > will not hurt fairness as most rwsem fairness concerns relate to
> > reader vs. writer fairness.
>
> Agreed, and I'm sure this will improve performance and may
> make this performance regression go away.
>
> David, is that Ok to you? If so, I may have a try.
I'm not David but please try it :-)
Making rwsem behavior and scalability similar to mutexes would
have numerous advantages.
> > Am I correct to assume that all relevant users in this
> > workload are down_write() users?
>
> Yes, as commit 5a50508 just convert all mutex to down_write.
A second track of inquiry would be to see whether any of the key
usage sites could be converted to down_read() or whether the
lock hold times could be reduced drastically - but I doubt
that's really possible on such heavily forking workloads.
Thanks,
Ingo
next prev parent reply other threads:[~2013-01-29 9:12 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-29 8:25 aim7 performance regression by commit 5a50508 report from LKP Yuanhan Liu
2013-01-29 8:44 ` Ingo Molnar
2013-01-29 9:06 ` Yuanhan Liu
2013-01-29 9:12 ` Ingo Molnar [this message]
2013-01-30 9:34 ` Yuanhan Liu
2013-01-31 11:22 ` Ingo Molnar
2013-02-01 10:53 ` Yuanhan Liu
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