From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CC77E13F6DFF for ; Mon, 30 Jul 2018 14:30:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7892F20893 for ; Mon, 30 Jul 2018 14:30:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7892F20893 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730592AbeG3QFp (ORCPT ); Mon, 30 Jul 2018 12:05:45 -0400 Received: from shelob.surriel.com ([96.67.55.147]:49762 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726860AbeG3QFp (ORCPT ); Mon, 30 Jul 2018 12:05:45 -0400 Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1fk9Bb-0000vJ-Ts; Mon, 30 Jul 2018 10:30:11 -0400 Message-ID: <1532961011.28585.30.camel@surriel.com> Subject: Re: [PATCH v2 11/11] mm,sched: conditionally skip lazy TLB mm refcounting From: Rik van Riel To: Peter Zijlstra Cc: Andy Lutomirski , LKML , kernel-team , X86 ML , Vitaly Kuznetsov , Ingo Molnar , Mike Galbraith , Dave Hansen , Catalin Marinas , Benjamin Herrenschmidt Date: Mon, 30 Jul 2018 10:30:11 -0400 In-Reply-To: <20180730095502.GG2494@hirez.programming.kicks-ass.net> References: <20180728215357.3249-1-riel@surriel.com> <20180728215357.3249-11-riel@surriel.com> <20180729155452.37eddc11@imladris.surriel.com> <20180730095502.GG2494@hirez.programming.kicks-ass.net> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-PiyL3ua32SMIGUwm91Kh" X-Mailer: Evolution 3.26.6 (3.26.6-1.fc27) Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-PiyL3ua32SMIGUwm91Kh Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2018-07-30 at 11:55 +0200, Peter Zijlstra wrote: > On Sun, Jul 29, 2018 at 03:54:52PM -0400, Rik van Riel wrote: > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index c45de46fdf10..11724c9e88b0 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -2691,7 +2691,7 @@ static struct rq *finish_task_switch(struct > > task_struct *prev) > > */ > > if (mm) { > > membarrier_mm_sync_core_before_usermode(mm); > > - mmdrop(mm); > > + drop_lazy_mm(mm); > > } > > if (unlikely(prev_state =3D=3D TASK_DEAD)) { > > if (prev->sched_class->task_dead) > > @@ -2805,7 +2805,7 @@ context_switch(struct rq *rq, struct > > task_struct *prev, > > */ > > if (!mm) { > > next->active_mm =3D oldmm; > > - mmgrab(oldmm); > > + grab_lazy_mm(oldmm); > > enter_lazy_tlb(oldmm, next); > > } else > > switch_mm_irqs_off(oldmm, mm, next); >=20 > 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: Date: Fri, 20 Jul 2018 11:32:39 +0200 From: Peter Zijlstra Subject: Re: [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Message-ID: <20180720093239.GO2494@hirez.programming.kicks-ass.net> + /* + * kernel -> kernel lazy + transfer active + * user -> kernel lazy + mmgrab() active + * + * kernel -> user switch + mmdrop() active + * user -> user switch + */ + if (!next->mm) { // to kernel + enter_lazy_tlb(prev->active_mm, next); + +#ifdef ARCH_NO_ACTIVE_MM + next->active_mm =3D prev->active_mm; + if (prev->mm) // from user + mmgrab(prev->active_mm); +#endif + } else { // to user + switch_mm_irqs_off(prev->active_mm, next->mm, next); + +#ifdef ARCH_NO_ACTIVE_MM + if (!prev->mm) { // from kernel + /* will mmdrop() in finish_task_switch(). */ + rq->prev_mm =3D prev->active_mm; + prev->active_mm =3D NULL; + } +#endif What email should I look for to find the thing you referenced above? > I agree with Andy that if you avoid the refcount fiddling, then you > should also not muck with active_mm. >=20 > That is, if you keep active_mm for now (which seems a reasonable > first > step) then at least ensure you keep ->mm =3D=3D ->active_mm at all times. There do not seem to be a lot of places left in arch/x86/ that reference active_mm. I guess the next patch series should excise those? :) --=20 All Rights Reversed. --=-PiyL3ua32SMIGUwm91Kh Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEKR73pCCtJ5Xj3yADznnekoTE3oMFAltfIPMACgkQznnekoTE 3oPx2QgAk7+QJQCkB3QiIOH6urIp0jk0HSIo8Lt+W7Gb9dKIaL3B0rJMYBavozwS 0jtUEn9gprCUYbG8XaDV10gVGLec7tbdV8bOLDWTEE9pG0JG1oOXtRuSkZTHnMGf RKs2l0ABMCxXQjhMQxAmpHcHc+/bImt/E47pLAymuNBsl/odW1yvBgKiXKxLEzIF rDE2tnbkx8cYhAjI+tzQC7EnzJ5Mo2CBt0FW/hlwQV6czRl+Dt/9crYuMO8FQa91 mJTWk7VVhFPyHnNYI+pNOtIcBwjyHCzFcMb/kWi87W4SP5QMYLKvACCUrg/TOvpM QELBfJarZCaLkk/waLfg4JOwvTtYCQ== =fMqg -----END PGP SIGNATURE----- --=-PiyL3ua32SMIGUwm91Kh--