From: Rik van Riel <riel@surriel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Mike Galbraith <efault@gmx.de>,
LKML <linux-kernel@vger.kernel.org>,
songliubraving@fb.com, kernel-team <kernel-team@fb.com>,
Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] x86,switch_mm: skip atomic operations for init_mm
Date: Fri, 01 Jun 2018 16:35:24 -0400 [thread overview]
Message-ID: <1527885324.7898.88.camel@surriel.com> (raw)
In-Reply-To: <CALCETrVE5ugmiSOjQ5sw7V+S4bRpMDs419rgrbTzfvjfhbWeqA@mail.gmail.com>
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On Fri, 2018-06-01 at 13:03 -0700, Andy Lutomirski wrote:
> Mike, you never did say: do you have PCID on your CPU? Also, what is
> your workload doing to cause so many switches back and forth between
> init_mm and a task.
>
> The point of the optimization is that switching to init_mm() should
> be
> fairly fast on a PCID system, whereas an IPI to do the deferred flush
> is very expensive regardless of PCID.
While I am sure that bit is true, Song and I
observed about 4x as much CPU use in the atomic
operations in cpumask_clear_cpu and cpumask_set_cpu
(inside switch_mm_irqs_off) as we saw CPU used
in the %cr3 reload itself.
Given how expensive those cpumask updates are,
lazy TLB mode might always be worth it, especially
on larger systems.
--
All Rights Reversed.
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next prev parent reply other threads:[~2018-06-01 20:35 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-01 12:28 [PATCH] x86,switch_mm: skip atomic operations for init_mm Rik van Riel
2018-06-01 15:11 ` Andy Lutomirski
2018-06-01 18:22 ` Rik van Riel
2018-06-01 18:48 ` Mike Galbraith
2018-06-01 19:43 ` Rik van Riel
2018-06-01 20:03 ` Andy Lutomirski
2018-06-01 20:35 ` Rik van Riel [this message]
2018-06-01 21:21 ` Andy Lutomirski
2018-06-01 22:13 ` Rik van Riel
2018-06-02 3:35 ` Andy Lutomirski
2018-06-02 5:04 ` Rik van Riel
2018-06-02 20:14 ` Andy Lutomirski
2018-06-03 0:51 ` Song Liu
2018-06-03 1:38 ` Rik van Riel
2018-06-06 18:17 ` Andy Lutomirski
2018-06-06 19:00 ` Rik van Riel
2018-06-06 19:23 ` Andy Lutomirski
2018-06-02 3:39 ` Mike Galbraith
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