From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2BB1C396582; Thu, 12 Mar 2026 20:13:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773346392; cv=none; b=R3mv+MiWtXejMBqpOB/2rGxoVAssXKT/lWtsxBJdL3AABWk6axuRkVKowgJIYWxKWn8QOymDf7iz0Ahy9thNdx3VCJLS4PVUGr4px7f1Z4VpOzirBQltgnrwAFbANXKCKFJ90+m7JzVs6PGiMkxwey9OR2UeVx7U4dNofEOnvc8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773346392; c=relaxed/simple; bh=JfX5ViT/E0csCibTlVhk1xajQ8nq48c62sRc3Rw9vgM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SNrOjbXBYhbEkvHHYuStR7C1xf8KwK6rG/iEf5GZp0n6pQK7Q+7q2wjsPZOceViPIIRbBckceZCH74hlO3bktC819CUv38zbpmu/MUdaaZOuvf2uXMZahY3eJic5RA0OVgkQtgS52gfxo8fyj3m0ZziGzHUxQfkXD4x6CK8d26I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=wmd3oBwF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="wmd3oBwF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A37BC4CEF7; Thu, 12 Mar 2026 20:13:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773346392; bh=JfX5ViT/E0csCibTlVhk1xajQ8nq48c62sRc3Rw9vgM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wmd3oBwFoHfkI6qEPrr9SWhPbDexE/FNSFoDQhQ+vqEQHZyL+93XjwwqmRJtbt/is q64+mwN4uVzgullxjjPyzZCOecZzajRU6ORmka4FYZQ3rtCR22THUJOroKOndRxYWu OHg2J+29wqJciT3jW07fS4KVwXU2OM0LAOCveBpo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Peter Zijlstra (Intel)" , Vincent Guittot , K Prateek Nayak , Shubhang Kaushik , Sasha Levin Subject: [PATCH 6.12 014/265] sched/fair: Fix lag clamp Date: Thu, 12 Mar 2026 21:06:41 +0100 Message-ID: <20260312201018.688522524@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260312201018.128816016@linuxfoundation.org> References: <20260312201018.128816016@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra [ Upstream commit 6e3c0a4e1ad1e0455b7880fad02b3ee179f56c09 ] Vincent reported that he was seeing undue lag clamping in a mixed slice workload. Implement the max_slice tracking as per the todo comment. Fixes: 147f3efaa241 ("sched/fair: Implement an EEVDF-like scheduling policy") Reported-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Tested-by: Vincent Guittot Tested-by: K Prateek Nayak Tested-by: Shubhang Kaushik Link: https://patch.msgid.link/20250422101628.GA33555@noisy.programming.kicks-ass.net Signed-off-by: Sasha Levin --- include/linux/sched.h | 1 + kernel/sched/fair.c | 39 +++++++++++++++++++++++++++++++++++---- 2 files changed, 36 insertions(+), 4 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index af143d3af85fa..9b722cf6ceb45 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -545,6 +545,7 @@ struct sched_entity { u64 deadline; u64 min_vruntime; u64 min_slice; + u64 max_slice; struct list_head group_node; unsigned char on_rq; diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bdb17a3b83f3d..4ffa0fdb61aa3 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -673,6 +673,8 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq) return cfs_rq->zero_vruntime + avg; } +static inline u64 cfs_rq_max_slice(struct cfs_rq *cfs_rq); + /* * lag_i = S - s_i = w_i * (V - v_i) * @@ -686,17 +688,16 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq) * EEVDF gives the following limit for a steady state system: * * -r_max < lag < max(r_max, q) - * - * XXX could add max_slice to the augmented data to track this. */ static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se) { + u64 max_slice = cfs_rq_max_slice(cfs_rq) + TICK_NSEC; s64 vlag, limit; SCHED_WARN_ON(!se->on_rq); vlag = avg_vruntime(cfs_rq) - se->vruntime; - limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se); + limit = calc_delta_fair(max_slice, se); se->vlag = clamp(vlag, -limit, limit); } @@ -764,6 +765,21 @@ static inline u64 cfs_rq_min_slice(struct cfs_rq *cfs_rq) return min_slice; } +static inline u64 cfs_rq_max_slice(struct cfs_rq *cfs_rq) +{ + struct sched_entity *root = __pick_root_entity(cfs_rq); + struct sched_entity *curr = cfs_rq->curr; + u64 max_slice = 0ULL; + + if (curr && curr->on_rq) + max_slice = curr->slice; + + if (root) + max_slice = max(max_slice, root->max_slice); + + return max_slice; +} + static inline bool __entity_less(struct rb_node *a, const struct rb_node *b) { return entity_before(__node_2_se(a), __node_2_se(b)); @@ -789,6 +805,15 @@ static inline void __min_slice_update(struct sched_entity *se, struct rb_node *n } } +static inline void __max_slice_update(struct sched_entity *se, struct rb_node *node) +{ + if (node) { + struct sched_entity *rse = __node_2_se(node); + if (rse->max_slice > se->max_slice) + se->max_slice = rse->max_slice; + } +} + /* * se->min_vruntime = min(se->vruntime, {left,right}->min_vruntime) */ @@ -796,6 +821,7 @@ static inline bool min_vruntime_update(struct sched_entity *se, bool exit) { u64 old_min_vruntime = se->min_vruntime; u64 old_min_slice = se->min_slice; + u64 old_max_slice = se->max_slice; struct rb_node *node = &se->run_node; se->min_vruntime = se->vruntime; @@ -806,8 +832,13 @@ static inline bool min_vruntime_update(struct sched_entity *se, bool exit) __min_slice_update(se, node->rb_right); __min_slice_update(se, node->rb_left); + se->max_slice = se->slice; + __max_slice_update(se, node->rb_right); + __max_slice_update(se, node->rb_left); + return se->min_vruntime == old_min_vruntime && - se->min_slice == old_min_slice; + se->min_slice == old_min_slice && + se->max_slice == old_max_slice; } RB_DECLARE_CALLBACKS(static, min_vruntime_cb, struct sched_entity, -- 2.51.0