linux-kernel - Re: [PATCH v2 11/11] mm,sched: conditionally skip lazy TLB mm refcounting

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Message-ID: <CALCETrXZPN6Lt55siHM__YW4jFfoy5w+Hd2aJtEi8qhsro6RMA@mail.gmail.com>
Date:   Mon, 30 Jul 2018 12:30:41 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Rik van Riel <riel@...riel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...com>, X86 ML <x86@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Dave Hansen <dave.hansen@...el.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v2 11/11] mm,sched: conditionally skip lazy TLB mm refcounting

On Mon, Jul 30, 2018 at 12:15 PM, Rik van Riel <riel@...riel.com> wrote:
> On Mon, 2018-07-30 at 18:26 +0200, Peter Zijlstra wrote:
>> On Mon, Jul 30, 2018 at 10:30:11AM -0400, Rik van Riel wrote:
>>
>> > > What happened to the rework I did there? That not only avoided
>> > > fiddling
>> > > with active_mm, but also avoids grab/drop cycles for the other
>> > > architectures when doing task->kthread->kthread->task things.
>> >
>> > I don't think I saw that. I only saw your email from
>> > July 20th with this fragment of code, which does not
>> > appear to avoid the grab/drop cycles, and still fiddles
>> > with active_mm:
>>
>> Yeah, that's it. Note how it doesn't do a grab+drop for kernel-
>> >kernel,
>> where the current could would have.
>>
>> And also note that it only fiddles with active_mm if it does the
>> grab+drop thing (the below should have s/ifdef/ifndef/ to make more
>> sense maybe).
>
> I'll kick off a test with your variant. I don't think we
> will see any performance difference on x86 (due to not
> using a refcount at all any more), but unless Ingo is in
> a hurry I guess there's no issue rewriting this part of
> the patch series :)
>
> Do the other patches look ok to you and Andy?
>

The whole series other than the active_mm stuff looked okay to me.