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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62908C4167B for ; Tue, 7 Nov 2023 09:07:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233773AbjKGJHa (ORCPT ); Tue, 7 Nov 2023 04:07:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51088 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229541AbjKGJH1 (ORCPT ); Tue, 7 Nov 2023 04:07:27 -0500 Received: from mail-il1-x129.google.com (mail-il1-x129.google.com [IPv6:2607:f8b0:4864:20::129]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3385B101 for ; Tue, 7 Nov 2023 01:07:00 -0800 (PST) Received: by mail-il1-x129.google.com with SMTP id e9e14a558f8ab-3575287211bso18784375ab.1 for ; Tue, 07 Nov 2023 01:07:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1699348019; x=1699952819; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=5WhtyOuoYTC7y8LDKEmQ/ZymxuVCiJ9n8cawTAnr7CM=; b=PYTtV0ZFmM1bebYpgz6OEjwztW+AexkOIbsl7ifPrRqVM+gbJsSE09N71BiKicfY+r E4mr754r3tyoZF0SvvUP5o7SWHE0v7vomORX5VqCltfXkYBkEJkexrRIBb22vXM1uYyw As+HqOnjRdCWLRlKDIVwUrMfEjUG/7B2YLATjzKK6pJ3d7Rp/bYynSaBNm7P/k56x0fW cyTgyuBhKK7yyay23n0PucPLcR4Yo5/526FwwunPwPBRERBOQpxj+r31VBocHzi69n+d /H0Svb+cNjF53FH+FAoYbq9GX5I8BidMgrT5E12DHbzaTJSrowNkr/ccrqReR9GD38/b z3xQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699348019; x=1699952819; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=5WhtyOuoYTC7y8LDKEmQ/ZymxuVCiJ9n8cawTAnr7CM=; b=taOGgxTKfCPDtfE4iWI0H9rmvgSwMhwcNtQCHKwROSdPwBp+PN3j5JE6yaZu4A1mZo PvAitET+2CZEBTAQhsDC8U3ywYPMzmuf0ZpiFUtV0nuKsNaFOy9Evn571Xl3K6KK/JDo rmOI7XlV9sNiZs1Y1+I9g1SqP/y3Pu/GHeBFWTv46pEAI8vEiVjQCEQa1Fgu2DX8Z0rK YCBujll/91LEtiA4hiZJ2nBXpBhOQYMtDn9wISaWG3AEZCQCdQnxKZiVpZfvMdxddAng kHcH7WKRtrIBtBR7jcwBlGXo0uxM1B7T4nqTE4aMXAtb19Yte0t6CzmXBUWlSMRBCYcn P/Wg== X-Gm-Message-State: AOJu0YxXU2mQzpdUTErkMjk2BI/aUod2OaNT1iADkDICtmE7DE+zjMWB oM91AU8pC8XTIjTJEjkdmqrnpQ== X-Google-Smtp-Source: AGHT+IEIZ7CTtj4Z+Mlik01+Ryk6gfGcuPZXNFyBQMW/QDE1hVQZIC30SBzzm50JmvGK9v+U9cx6kQ== X-Received: by 2002:a05:6e02:1c22:b0:359:4726:9017 with SMTP id m2-20020a056e021c2200b0035947269017mr2718352ilh.15.1699348019547; Tue, 07 Nov 2023 01:06:59 -0800 (PST) Received: from C02DV8HUMD6R.bytedance.net ([203.208.167.147]) by smtp.gmail.com with ESMTPSA id k27-20020a63ba1b000000b005ab7b055573sm875154pgf.79.2023.11.07.01.06.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Nov 2023 01:06:59 -0800 (PST) From: Abel Wu To: Peter Zijlstra , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Valentin Schneider Cc: Barry Song <21cnbao@gmail.com>, Benjamin Segall , Chen Yu , Daniel Jordan , "Gautham R . Shenoy" , Joel Fernandes , K Prateek Nayak , Mike Galbraith , Qais Yousef , Tim Chen , Yicong Yang , Youssef Esmat , linux-kernel@vger.kernel.org, Abel Wu Subject: [PATCH 1/4] sched/eevdf: Fix vruntime adjustment on reweight Date: Tue, 7 Nov 2023 17:05:07 +0800 Message-Id: <20231107090510.71322-2-wuyun.abel@bytedance.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20231107090510.71322-1-wuyun.abel@bytedance.com> References: <20231107090510.71322-1-wuyun.abel@bytedance.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org vruntime of the (on_rq && !0-lag) entity needs to be adjusted when it gets re-weighted, and the calculations can be simplified based on the fact that re-weight won't change the w-average of all the entities. Please check the proofs in comments. But adjusting vruntime can also cause position change in RB-tree hence require re-queue to fix up which might be costly. This might be avoided by deferring adjustment to the time the entity actually leaves tree (dequeue/pick), but that will negatively affect task selection and probably not good enough either. Fixes: 147f3efaa241 ("sched/fair: Implement an EEVDF-like scheduling policy") Signed-off-by: Abel Wu --- kernel/sched/fair.c | 151 +++++++++++++++++++++++++++++++++++++------- 1 file changed, 128 insertions(+), 23 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8767988242ee..b00d09a9b601 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3666,41 +3666,140 @@ static inline void dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { } #endif +static void reweight_eevdf(struct cfs_rq *cfs_rq, struct sched_entity *se, + unsigned long weight) +{ + unsigned long old_weight = se->load.weight; + u64 avruntime = avg_vruntime(cfs_rq); + s64 vlag, vslice; + + /* + * VRUNTIME + * ======== + * + * COROLLARY #1: The virtual runtime of the entity needs to be + * adjusted if re-weight at !0-lag point. + * + * Proof: For contradiction assume this is not true, so we can + * re-weight without changing vruntime at !0-lag point. + * + * Weight VRuntime Avg-VRuntime + * before w v V + * after w' v' V' + * + * Since lag needs to be preserved through re-weight: + * + * lag = (V - v)*w = (V'- v')*w', where v = v' + * ==> V' = (V - v)*w/w' + v (1) + * + * Let W be the total weight of the entities before reweight, + * since V' is the new weighted average of entities: + * + * V' = (WV + w'v - wv) / (W + w' - w) (2) + * + * by using (1) & (2) we obtain: + * + * (WV + w'v - wv) / (W + w' - w) = (V - v)*w/w' + v + * ==> (WV-Wv+Wv+w'v-wv)/(W+w'-w) = (V - v)*w/w' + v + * ==> (WV - Wv)/(W + w' - w) + v = (V - v)*w/w' + v + * ==> (V - v)*W/(W + w' - w) = (V - v)*w/w' (3) + * + * Since we are doing at !0-lag point which means V != v, we + * can simplify (3): + * + * ==> W / (W + w' - w) = w / w' + * ==> Ww' = Ww + ww' - ww + * ==> W * (w' - w) = w * (w' - w) + * ==> W = w (re-weight indicates w' != w) + * + * So the cfs_rq contains only one entity, hence vruntime of + * the entity @v should always equal to the cfs_rq's weighted + * average vruntime @V, which means we will always re-weight + * at 0-lag point, thus breach assumption. Proof completed. + * + * + * COROLLARY #2: Re-weight does NOT affect weighted average + * vruntime of all the entities. + * + * Proof: According to corollary #1, Eq. (1) should be: + * + * (V - v)*w = (V' - v')*w' + * ==> v' = V' - (V - v)*w/w' (4) + * + * According to the weighted average formula, we have: + * + * V' = (WV - wv + w'v') / (W - w + w') + * = (WV - wv + w'(V' - (V - v)w/w')) / (W - w + w') + * = (WV - wv + w'V' - Vw + wv) / (W - w + w') + * = (WV + w'V' - Vw) / (W - w + w') + * + * ==> V'*(W - w + w') = WV + w'V' - Vw + * ==> V' * (W - w) = (W - w) * V (5) + * + * If the entity is the only one in the cfs_rq, then reweight + * always occurs at 0-lag point, so V won't change. Or else + * there are other entities, hence W != w, then Eq. (5) turns + * into V' = V. So V won't change in either case, proof done. + * + * + * So according to corollary #1 & #2, the effect of re-weight + * on vruntime should be: + * + * v' = V' - (V - v) * w / w' (4) + * = V - (V - v) * w / w' + * = V - vl * w / w' + * = V - vl' + */ + if (avruntime != se->vruntime) { + vlag = (s64)(avruntime - se->vruntime); + vlag = div_s64(vlag * old_weight, weight); + se->vruntime = avruntime - vlag; + } + + /* + * DEADLINE + * ======== + * + * When the weight changes, the virtual time slope changes and + * we should adjust the relative virtual deadline accordingly. + * + * d' = v' + (d - v)*w/w' + * = V' - (V - v)*w/w' + (d - v)*w/w' + * = V - (V - v)*w/w' + (d - v)*w/w' + * = V + (d - V)*w/w' + */ + vslice = (s64)(se->deadline - avruntime); + vslice = div_s64(vslice * old_weight, weight); + se->deadline = avruntime + vslice; +} + static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, unsigned long weight) { - unsigned long old_weight = se->load.weight; + bool curr = cfs_rq->curr == se; if (se->on_rq) { /* commit outstanding execution time */ - if (cfs_rq->curr == se) + if (curr) update_curr(cfs_rq); else - avg_vruntime_sub(cfs_rq, se); + __dequeue_entity(cfs_rq, se); update_load_sub(&cfs_rq->load, se->load.weight); } dequeue_load_avg(cfs_rq, se); - update_load_set(&se->load, weight); - if (!se->on_rq) { /* * Because we keep se->vlag = V - v_i, while: lag_i = w_i*(V - v_i), * we need to scale se->vlag when w_i changes. */ - se->vlag = div_s64(se->vlag * old_weight, weight); + se->vlag = div_s64(se->vlag * se->load.weight, weight); } else { - s64 deadline = se->deadline - se->vruntime; - /* - * When the weight changes, the virtual time slope changes and - * we should adjust the relative virtual deadline accordingly. - */ - deadline = div_s64(deadline * old_weight, weight); - se->deadline = se->vruntime + deadline; - if (se != cfs_rq->curr) - min_deadline_cb_propagate(&se->run_node, NULL); + reweight_eevdf(cfs_rq, se, weight); } + update_load_set(&se->load, weight); + #ifdef CONFIG_SMP do { u32 divider = get_pelt_divider(&se->avg); @@ -3712,8 +3811,17 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, enqueue_load_avg(cfs_rq, se); if (se->on_rq) { update_load_add(&cfs_rq->load, se->load.weight); - if (cfs_rq->curr != se) - avg_vruntime_add(cfs_rq, se); + if (!curr) { + /* + * The entity's vruntime has been adjusted, so let's check + * whether the rq-wide min_vruntime needs updated too. Since + * the calculations above require stable min_vruntime rather + * than up-to-date one, we do the update at the end of the + * reweight process. + */ + __enqueue_entity(cfs_rq, se); + update_min_vruntime(cfs_rq); + } } } @@ -3857,14 +3965,11 @@ static void update_cfs_group(struct sched_entity *se) #ifndef CONFIG_SMP shares = READ_ONCE(gcfs_rq->tg->shares); - - if (likely(se->load.weight == shares)) - return; #else - shares = calc_group_shares(gcfs_rq); + shares = calc_group_shares(gcfs_rq); #endif - - reweight_entity(cfs_rq_of(se), se, shares); + if (unlikely(se->load.weight != shares)) + reweight_entity(cfs_rq_of(se), se, shares); } #else /* CONFIG_FAIR_GROUP_SCHED */ -- 2.37.3