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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 E5905C433ED for ; Fri, 7 May 2021 06:53:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A6825613D6 for ; Fri, 7 May 2021 06:53:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232012AbhEGGyf (ORCPT ); Fri, 7 May 2021 02:54:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39368 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232391AbhEGGyX (ORCPT ); Fri, 7 May 2021 02:54:23 -0400 Received: from mail-lj1-x22e.google.com (mail-lj1-x22e.google.com [IPv6:2a00:1450:4864:20::22e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7C8E1C061761 for ; Thu, 6 May 2021 23:53:21 -0700 (PDT) Received: by mail-lj1-x22e.google.com with SMTP id u25so10217545ljg.7 for ; Thu, 06 May 2021 23:53:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=xD6sT+JoVSfHAJgyHKvC2drKSKBvndrhIf3suCNO9U0=; b=Ur4W10ESfKgAsSrMSfPBFPUOmYjGYZdTxDdFX5nEtQUE1Hgiz7XNRiNtVeS/IuppA+ yXaXQLGW1r3RsDp5UOGvdW69ziAlq83u4opBBm+u5ppSN/fyJ3mjhsNLQ3GazbMFdqzd Gv47C1At9vf6mPt2NQEpHoY2GS5aXLMA7KqgV5t1LL/3B62N8qONOGIlA+U3ca2lszkV 1dxdIvsJ/n0oyABRLZJgcdpfdYMTQT4JNoSm72+2xRBh3dOo1mDyOIpKFhlIhquynvFh lpdiyORMJ24LUfAkzLW/U1PGgW+OnSpPhArNKfRGKnBFiwK4wieHYexmUv77zPvfyDnW MrYw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=xD6sT+JoVSfHAJgyHKvC2drKSKBvndrhIf3suCNO9U0=; b=YkoEGsKN+i07O4nU81L5HI7uoIfNfWChFw0FiMN9VsFTNxghlxDWYzifgOQKzm4uiJ PSaaZHpDvxVu/WQkrElu4BmHQAGkvwH6E3VeWoPNlVNHudSn6ZiFHQ/aBEBrVAAouhFq aLxqiBPYmEco25OnamZYGL1jQoVnnMRi6t6FcqEgqcAPx+Kw5zPirYZ/B1rQsKfDVksw GJZFmU8GWexzIE4Alb9E/NI2M1MJKBX5koT+3iO1EeWqPGkcr8Ge/GtYDWJ1ChUkqSPj xRjoIJwXAalPKbyjLsLM9IMuDYgU5elLrTGMA5Q52LjtbWMPmbrYvYrpzizZWFVksUv7 +Ndg== X-Gm-Message-State: AOAM531dfF/WsSVYEMlDfJcrwWtIup6+Z7ei4Si1wEIppBiiDXZV4xLn kGZmDzxhWoXPmavuwOclTib3p4pH/FA9GLUFh61nsQ== X-Google-Smtp-Source: ABdhPJy7WgIvZKSzC0a4yMw9D+ZV4r8X/MS85vT3kBT61bVu3xHBKsPg4BC50LXkkiUty0rnn6OywjkMRhQktmm4F94= X-Received: by 2002:a2e:8557:: with SMTP id u23mr6438212ljj.221.1620370399951; Thu, 06 May 2021 23:53:19 -0700 (PDT) MIME-Version: 1.0 References: <20210506110936.8797-1-xuewen.yan94@gmail.com> <20210506122823.GA8671@ubiquitous> <20210506162600.GA11916@ubiquitous> In-Reply-To: From: Vincent Guittot Date: Fri, 7 May 2021 08:53:08 +0200 Message-ID: Subject: Re: [PATCH] sched/pelt: Add UTIL_AVG_UNCHANGED flag for last_enqueued_diff To: Xuewen Yan Cc: Vincent Donnefort , Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Benjamin Segall , Mel Gorman , Daniel Bristot de Oliveira , linux-kernel , Chunyan Zhang , Ryan Y Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 7 May 2021 at 03:36, Xuewen Yan wrote: > > On Fri, May 7, 2021 at 12:26 AM Vincent Donnefort > wrote: > > > > On Thu, May 06, 2021 at 08:46:08PM +0800, Xuewen Yan wrote: > > > Hi > > > On Thu, May 6, 2021 at 8:28 PM Vincent Donnefort > > > wrote: > > > > > > > > On Thu, May 06, 2021 at 07:09:36PM +0800, Xuewen Yan wrote: > > > > > From: Xuewen Yan > > > > > > > > > > The UTIL_AVG_UNCHANGED flag had been cleared when the task util c= hanged. > > > > > And the enqueued is equal to task_util with the flag, so it is be= tter > > > > > to add the UTIL_AVG_UNCHANGED flag for last_enqueued_diff. > > > > Could we change the description here a bit? I don't think this is accur= ately > > explaning the issue. Would probably be interesting to mention that by n= ot > > setting the flag, which is the LSB, we add +1 to the diff. This is ther= efore > > reducing slightly UTIL_EST_MARGIN. > > ok, If you agree with this patch, I'll change it in V2. Although the impact is not significant , it's worth having an accurate computation. So the patch makes sense to me. Please submit a v2 > > > > > > > > > > > > Fixes: b89997aa88f0b sched/pelt: Fix task util_est update filteri= ng > > > > > > > > > > Signed-off-by: Xuewen Yan > > > > > --- > > > > > kernel/sched/fair.c | 2 +- > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > > > index e5e457fa9dc8..94d77b4fa601 100644 > > > > > --- a/kernel/sched/fair.c > > > > > +++ b/kernel/sched/fair.c > > > > > @@ -3996,7 +3996,7 @@ static inline void util_est_update(struct c= fs_rq *cfs_rq, > > > > > if (ue.enqueued & UTIL_AVG_UNCHANGED) > > > > > return; > > > > > > > > > > - last_enqueued_diff =3D ue.enqueued; > > > > > + last_enqueued_diff =3D (ue.enqueued | UTIL_AVG_UNCHANGED); > > > > > > > > > > /* > > > > > * Reset EWMA on utilization increases, the moving average = is used only > > > > > -- > > > > > 2.29.0 > > > > > > > > > > > > > Hi, > > > > > > > > We do indeed for the diff use the flag for the value updated and no= flag for the > > > > value before the update. However, last_enqueued_diff is only used f= or the margin > > > > check which is an heuristic and is not an accurate value (~1%) and = as we know > > > The last_enqueued_diff is compared with the UTIL_EST_MARGIN which is > > > "1024/100 =3D 10", > > > and The LSB may cause ~10% error. > > > > I meant ~1% being the original margin. With the bit set, we would use 0= .87% instead > > of 0.97%. > > Because the within_margin() does not contain =E2=80=9C=3D=E2=80=9D=EF=BC= =8C if the enqueued > without the flag, the margin may be 0.97%(10/1024), > with the flag, be 1.07%(11/1024) instead of 0.87% I think. > > > > > > we already loose the LSB in util_est, I'm not sure this is really n= ecessary. > > > I'm also not very sure, maybe the calculation will be more rigorous > > > with the flag? > > > > > > > > -- > > > > Vincent > > > >