linux-kernel - Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path

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Date:	Tue, 1 Oct 2013 09:48:02 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Waiman Long <Waiman.Long@...com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Alex Shi <alex.shi@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Sat, Sep 28, 2013 at 11:55:26AM -0700, Linus Torvalds wrote:
> > So if the primary reason for this is really just that f*cking anon_vma
> > lock, then I would seriously suggest:
> 
> I would still like to see the rwsem patches merged; even if we end up 
> going back to a spin style anon_vma lock.
> 
> There's been various reports in the past about how programs are 
> significantly faster if they wrap their mmap() calls in a pthread_mutex. 
> And this was purely down to the fact that rwsem writer-writer contention 
> blows chunks.

That's about the mm->mmap_sem rwsem, right?

That impact would have to be measured carefully, and not just for 
workloads where we know that better contention logic helps, but other MM 
workloads that are hitting hard on mmap_sem.

Thanks,

	Ingo
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