linux-kernel - Re: [PATCH 1/7] x86/mm/tlb: Always use lazy TLB mode

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Message-ID: <b1e2648c6fe01eb160b6817a4d7ff37109d806ef.camel@surriel.com>
Date:   Mon, 01 Oct 2018 12:07:12 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        will.deacon@....com, songliubraving@...com, mingo@...nel.org,
        luto@...nel.org, hpa@...or.com, npiggin@...il.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>, efault@....de
Subject: Re: [PATCH 1/7] x86/mm/tlb: Always use lazy TLB mode

On Mon, 2018-10-01 at 17:58 +0200, Peter Zijlstra wrote:
> On Tue, Sep 25, 2018 at 11:58:38PM -0400, Rik van Riel wrote:
> > Now that CPUs in lazy TLB mode no longer receive TLB shootdown
> > IPIs, except
> > at page table freeing time, and idle CPUs will no longer get
> > shootdown IPIs
> > for things like mprotect and madvise, we can always use lazy TLB
> > mode.
> 
> But that's only so at the end of this patch series; either change the
> Changelog or the location of this patch?

You are right, I should remove that from the changelog.

Want me to resend, or would you like to just replace
it with something like this:

"On most workloads, the number of context switches
far exceeds the number of TLB flushes sent. Optimizing
the context switches, by always using lazy TLB mode,
speeds up those workloads.

This patch results in about a 1% reduction in CPU use
on a two socket Broadwell system running a memcache
like workload."

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