From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f50.google.com (mail-pj1-f50.google.com [209.85.216.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9637E30C164 for ; Fri, 12 Jun 2026 01:34:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781228049; cv=none; b=iZ6e3pbqSXccqOONLn8Q8YjjRcgWXG7cJZUMUvcyV0P6jhAih1naTDw3aPllaRdmJCNkCJCesowFLCkMOaczD3RFmMbXj3pXvrfpwziYfRL3N1iteMfx/2/INqZpc0/gJctokLkT4jMvPEj8fYiNTCudGsUoFi58t0C0xlmD+us= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781228049; c=relaxed/simple; bh=Emd0iAge1yJWElgbu72y/eRXkT0AFDOYInOspeDoNXE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Y1xnctsCbrKpc4dEVsjiCtj42A0dEGAVlo2L5xLsJCBcxKyLuOdfmkyDu3Pd4PoQIEYVS39d3a8LLHRT3fl3rO0oM65BfCIwQnJebVNrzaSZlKT1n80nieXn5x11+jOLYYTBjt/Affl+Dh+QIVHInf0P0mbNAkPWlnLBXGiX+/0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=Mx7SEPvT; arc=none smtp.client-ip=209.85.216.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Mx7SEPvT" Received: by mail-pj1-f50.google.com with SMTP id 98e67ed59e1d1-372b4330deeso363476a91.0 for ; Thu, 11 Jun 2026 18:34:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1781228048; x=1781832848; 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=GBO/Qu5vraFOfUtlMrr746hyyKYTO/nlkxX0iKEt41I=; b=Mx7SEPvT6ftiZJwmGE0vNr1bnUeB1WCAAuRI1TrS8AkC196vyzqfD75RR2LhK3noQY rEAyxvxr7mFEFlhOuxUNMSA+Rc17SREMsjVIs65o1OSBcZqB5kFDNktv6XsCBe1nhPu+ 6o8yDHROIbNYWVUWet7pt2SNf452P7csfpH1JJ3Ao18carrxF9uQSwR1PSLgV4QXf0Ri wKg4zuZbr0Xof+ppwy91U5FcVEe0tvFUyf3kc0jvAWY6e2G0FP6RzO0U1AaAZNWp7Mit 6eTpFQr6lIDJOY4P6T8zCoBlDfj2e2yYnMXx7yrndyiaaPW3J61kU75+W/reTWh/O397 IMWg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781228048; x=1781832848; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=GBO/Qu5vraFOfUtlMrr746hyyKYTO/nlkxX0iKEt41I=; b=KVlFLgTHNh/pofWRyzNZHQVs53JwX+U7Mi6P/5RjslgAx9dxd7HjLgEfs5U4HHXJNA Yoa2sYg0OeNFBbiG/Tmh1R571R+DkV5fduziy33c0vx1xMYPYNsxd4RYrVdeA+5zT0VE 3N55a9/Nlg3ALbdjxB3fKgOH7vbFa2go5m0y9WQutyCjLlKpKGKRVmZS192FVzCdzOuj dlTdjl1tOM48dtcisb6bniqubghdyXfgjvQCqEx9vqROmH5ybOOynhiD/A6kz4aVv9Mh dSkZeQuXnhtHkyGzOO1shqmqcKwv954zfq5JSXKh07Wi1nOdaroO7thXj4nTWjKqo0hO Wu1g== X-Forwarded-Encrypted: i=1; AFNElJ+QmDZALU5ZR4jQVv/TQogwk974Jao8FZWwKBT1uZEx9D1gklZOytbZtudobs1swbfxiK8=@vger.kernel.org X-Gm-Message-State: AOJu0YwICT8b8OthrR3peItKdIYloanBUzGISVJ65JQysp0YuMnZtBwC GTkOGoEwURaui/XRG7u3Z46q9utED5MJbImgqxRxy0qI8IGSsbtz1WLN X-Gm-Gg: Acq92OHH3CuS2uZTrfYvKMuREBQDfwuTlkVbQXpsJGu7gHcM83+efINhVcDBqEvOSYc szZMUuYiSJHTACXJ6uioP4+V1lO/gVFi4hNR4DmBI1IVcRpGH+XBY7JCfS7G3HFzTU783NwjXEN 6nAopcHeaqiwHC6VGr0e7SSFxO0iiEnlW7UXrFGrul7U9xAD42jwM3s4OwxQ28yfGA99fGc7q4O cuZiBT6w39pUo6EF+MF4wDmlxGfsxPf75SIhufe3uFQaAXaTtlsb/cOKqiCv4SmKBz6Q5hqPS71 CbrtN3vvntWiKoaIuxAo2ea8NVwG3ikGZAAGyXMNZ6f10zH7OGu2Ehc2CFwzrSolTCBugMlHl03 Oew/COphYPCsfPHJTnexlmxx1fTsFq3P+5msAegRjpgABb+JwICXHxY3lMyARsV9zX5Q21JwdfC 7sL4Ywm8i2GtNiAEW+aXubcTL5Pq2pP60lKWLo X-Received: by 2002:a17:90b:4d0d:b0:36a:7da3:266b with SMTP id 98e67ed59e1d1-37a041af2b9mr898338a91.21.1781228047848; Thu, 11 Jun 2026 18:34:07 -0700 (PDT) Received: from wanpengli.. ([2408:822f:1aba:84a0:651:104c:ba0c:1f4a]) by smtp.googlemail.com with ESMTPSA id 98e67ed59e1d1-37a1f07bbfdsm250713a91.5.2026.06.11.18.34.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Jun 2026 18:34:07 -0700 (PDT) From: Wanpeng Li To: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Paolo Bonzini , Sean Christopherson Cc: K Prateek Nayak , Christian Borntraeger , Steven Rostedt , Vincent Guittot , Juri Lelli , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Wanpeng Li , Richie Buturla Subject: [PATCH v3 01/10] sched/fair: Add EEVDF lag credit primitive for nominated next-buddy Date: Fri, 12 Jun 2026 09:33:46 +0800 Message-ID: <20260612013355.59231-2-kernellwp@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260612013355.59231-1-kernellwp@gmail.com> References: <20260612013355.59231-1-kernellwp@gmail.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Wanpeng Li pick_eevdf()'s PICK_BUDDY path only returns cfs_rq->next when the entity is eligible. A yield_to() target that is behind avg_vruntime at any level of its sched_entity hierarchy is skipped, and the set_next_buddy() hint is lost. Add eevdf_credit_entity_vlag(), which can credit a nominated entity up to the eligibility boundary so that pick_eevdf() can honor the buddy hint. The helper handles cfs_rq->curr, which is off-tree and can be shifted in place while carrying any active vprot window. Gate the helper behind SCHED_FEAT(YIELD_TO_LAG_CREDIT). The helper has no caller in this change, so mark it __maybe_unused; there is no functional change. Signed-off-by: Wanpeng Li --- kernel/sched/fair.c | 48 +++++++++++++++++++++++++++++++++++++++++ kernel/sched/features.h | 9 ++++++++ 2 files changed, 57 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3ebec186f982..e7f5ea25fdae 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9341,6 +9341,54 @@ static void put_prev_task_fair(struct rq *rq, struct task_struct *prev, struct t } } +/* + * eevdf_credit_entity_vlag - credit a nominated next-buddy to eligibility + * + * Advance @se (already nominated by set_next_buddy(), so cfs_rq->next == se) + * just enough negative vlag to reach the eligibility boundary (vlag = 0) so + * pick_eevdf()'s PICK_BUDDY branch returns it. cfs_rq->curr is shifted in + * place (off-tree, carrying any vprot window). Queued entities are left + * unchanged. + * + * Idempotent: a no-op once @se is already eligible. Caller must hold + * rq_of(cfs_rq)->lock with rq_clock up to date. + */ +static void __maybe_unused +eevdf_credit_entity_vlag(struct cfs_rq *cfs_rq, struct sched_entity *se) +{ + u64 avruntime, credit; + s64 vlag; + + /* Callers gate this helper with YIELD_TO_LAG_CREDIT. */ + if (cfs_rq->nr_queued < 2) + return; + if (throttled_hierarchy(cfs_rq)) + return; + if (WARN_ON_ONCE(!se->on_rq) || se->sched_delayed) + return; + + update_curr(cfs_rq); + avruntime = avg_vruntime(cfs_rq); + vlag = entity_lag(cfs_rq, se, avruntime); + + /* Already eligible: nothing to do. */ + if (vlag >= 0) + return; + + credit = (u64)(-vlag); + + if (cfs_rq->curr == se) { + /* curr is off-tree: in-place shift, carrying any vprot window. */ + if (protect_slice(se)) + se->vprot -= credit; + se->vruntime -= credit; + se->deadline -= credit; + return; + } + + /* Queued entities are left unchanged by this helper path. */ +} + /* * sched_yield() is very simple */ diff --git a/kernel/sched/features.h b/kernel/sched/features.h index 84c4fe3abd74..65c511c9ca28 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -40,6 +40,15 @@ SCHED_FEAT(NEXT_BUDDY, false) */ SCHED_FEAT(PICK_BUDDY, true) +/* + * Let yield_to_task_fair() credit bounded EEVDF lag to the nominated + * next-buddy so pick_eevdf() honors the hint even when the target has + * negative vlag at some level of its ancestor chain. The credit is bounded + * by a queue-depth-scaled margin within entity_lag()'s legal range, so + * fairness is preserved. + */ +SCHED_FEAT(YIELD_TO_LAG_CREDIT, true) + /* * Consider buddies to be cache hot, decreases the likeliness of a * cache buddy being migrated away, increases cache locality. -- 2.43.0