linux-kernel - Re: TLB evaluation for Linux

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Message-ID: <960293705.209651220367565443.JavaMail.osg@osgjas01.cns.ufl.edu>
Date:	Tue, 2 Sep 2008 10:59:25 -0400 (EDT)
From:	"CHADHA,VINEET" <vineet@....edu>
To:	Arjan van de Ven <arjan@...radead.org>,
	"CHADHA,VINEET" <vineet@....edu>
Cc:	nickpiggin@...oo.com.au, linux-kernel@...r.kernel.org
Subject: Re: TLB evaluation for Linux


On Tue Sep 02 09:43:53 EDT 2008, Arjan van de Ven 
<arjan@...radead.org> wrote:

> On Tue, 2 Sep 2008 00:12:03 -0400 (EDT)
> "CHADHA,VINEET" <vineet@....edu> wrote:
> 

> note that linux only does an ipi to processors that actually are
> currently running a thread of the same program (or a kernel 
> thread).
> Old versions didn't do this (they also IPI'd idle processors), 
> but
> on modern cpus and modern kernels that's not supposed to happen 
> anymore
> (the C-states that flush the tlb anyway now do the kernel side
> bookkeeping as well to avoid the wakeup+useless flush)

Interesting to know about it.

> one of the problems is that invlpg is rather expensive; in 
> long-ago
> experiments the threshold was like around a handful of pages 
> already.
> At that point.. all the bookkeeping isn't likely to be a win.
> Esp since a tlb refill on x86 is quite cheap.

Yeah that is possible. Do you have link to any published work ? It 
would be still interesting to characterize and  compare behavior 
for new workloads scenarios such as virtual machines.

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