linux-kernel - Re: sched: softlockups in multi_cpu

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Date:	Fri, 06 Mar 2015 12:00:00 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Jason Low <jason.low2@...com>, Ingo Molnar <mingo@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...emonkey.org.uk>
Subject: Re: sched: softlockups in multi_cpu_stop

On Fri, 2015-03-06 at 11:55 -0800, Davidlohr Bueso wrote:
> On Fri, 2015-03-06 at 11:32 -0800, Linus Torvalds wrote:
> 
> > IOW, I wonder if we could special-case the common non-IO
> > fault-handling path something along the lines of:
> > 
> >  - look up the vma in the vma lookup cache
> 
> But you'd still need mmap_sem there to at least get the VMA's first
> value.

Incomplete msg... what I'm getting at is that one way or another
mmap_sem contention is easy to hit -- yes, avoiding it in IO paths is
obviously good for hold times. But I also think that it protects way too
much, ie making pthread intense workloads really suck as well.

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