linux-kernel - Re: 4.13..4.14 scheduling overhead regression (bisected

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Message-ID: <1527879389.7898.84.camel@surriel.com>
Date:   Fri, 01 Jun 2018 14:56:29 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: 4.13..4.14 scheduling overhead regression (bisected  -
 b956575bed91)

On Fri, 2018-06-01 at 15:20 +0200, Peter Zijlstra wrote:
> On Fri, Jun 01, 2018 at 02:57:53PM +0200, Mike Galbraith wrote:
> > b956575bed91ecfb136a8300742ecbbf451471ab is the first bad commit
> > commit b956575bed91ecfb136a8300742ecbbf451471ab
> > Author: Andy Lutomirski <luto@...nel.org>
> > Date:   Mon Oct 9 09:50:49 2017 -0700
> > 
> >     x86/mm: Flush more aggressively in lazy TLB mode
> 
> Oh boy... Maybe we should start looking at that optimization Andy
> mentioned.
> 
> IIRC all page freeing does indeed go through tlb_remove_page(), it
> shouldn't be too hard to make that work.

Page freeing does. However, page table freeing
does not, and might need to be done in a different
way.

I wonder how expensive/effective it would be to free
page tables with RCU, and have the RCU code flush the
TLB if it notices the ctx_id is wrong?

Also, I need to go find Andy's optimization, and
see how it works :)

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