From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 342B93D3D1B; Thu, 17 Sep 2026 17:50:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789667451; cv=none; b=uhmI7vIl1Ug05q4iZEgc6BPjcAImHVroS9qsTNMxev5zmgS7uk0BzPy37QOT/yXTlaqF6AsMMgIGipj0y1Bg7ea38XG5E/2aDYGOD2SOdTDwuYf7HXdhBhH8Z6GEv/GMG2kXYRflnw4H28CjvKB1yVsEEmzwRk9/pefQ17qNSf0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789667451; c=relaxed/simple; bh=kBbafnsGATfYcPa2656k68pfUGVmrvU4O6TQq4qzcQw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Skb4TT2L5EoBINFGUOxNtN/SBU2XQ5BPP7VJDraYeqrUPLiDu/a2Dx0OTwGfFNqnTENcCJT79UGck2F0pzJGqNuO5fN4EF5/VzAYNAKyUNh2nOnYcb1ZN0ufCOboym5scbYWcBA1GRZO3ihXq8+Ks2ng7eyB/JHn10B/ivKTSkU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ioyw3+rw; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ioyw3+rw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 705511F000FF; Thu, 17 Sep 2026 17:50:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789667450; bh=XC6XkxzQa8e0KxOgczBTQR0TpA0ZAxrKw//JzhbMmJg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ioyw3+rwku405i4YcpgYnoa/sKBP1bcK1+KqhCcsJzUskpweiwq6zKKt1h3UHcoAa Cw0KHt08JB4yKYY5mN+wF7ShCXzEq2TbPlb1ug+zOhGj24b4hCps7Gvb5/gjPstBUb aiR3r2Fy3Xwyl1RzU7ZxfxLBCRunoUn9upBw3Y6s= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Felix Abecassis , Andrea Righi , "Peter Zijlstra (Intel)" , Vincent Guittot , Sasha Levin Subject: [PATCH 6.12 0098/1102] sched/fair: Reject misfit pulls onto busy SMT siblings on asym-capacity Date: Thu, 17 Sep 2026 16:00:41 +0100 Message-ID: <20260917151541.953937096@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151539.408551884@linuxfoundation.org> References: <20260917151539.408551884@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev 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: Andrea Righi [ Upstream commit bf6aa722198d3c06e4236e8c5a480f30a64e1513 ] When SD_ASYM_CPUCAPACITY load balancing considers pulling a misfit task, capacity_of(dst_cpu) can overstate available compute if the SMT sibling is busy: the core does not deliver its full nominal capacity. If SMT is active and dst_cpu is not on a fully idle core, skip this destination so we do not migrate a misfit expecting a capacity upgrade we cannot actually provide. Reported-by: Felix Abecassis Signed-off-by: Andrea Righi Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Link: https://patch.msgid.link/20260509180955.1840064-5-arighi@nvidia.com Signed-off-by: Sasha Levin --- kernel/sched/fair.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 616ad9f86b228..011786704297c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9340,6 +9340,7 @@ struct lb_env { int dst_cpu; struct rq *dst_rq; + bool dst_core_idle; struct cpumask *dst_grpmask; int new_dst_cpu; @@ -10530,10 +10531,16 @@ static bool update_sd_pick_busiest(struct lb_env *env, * We can use max_capacity here as reduction in capacity on some * CPUs in the group should either be possible to resolve * internally or be covered by avg_load imbalance (eventually). + * + * When SMT is active, only pull a misfit to dst_cpu if it is on a + * fully idle core; otherwise the effective capacity of the core is + * reduced and we may not actually provide more capacity than the + * source. */ if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && (sgs->group_type == group_misfit_task) && - (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) || + (!env->dst_core_idle || + !capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) || sds->local_stat.group_type != group_has_spare)) return false; @@ -11099,6 +11106,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd unsigned long sum_util = 0; bool sg_overloaded = 0, sg_overutilized = 0; + env->dst_core_idle = !sched_smt_active() || is_core_idle(env->dst_cpu); + do { struct sg_lb_stats *sgs = &tmp_sgs; int local_group; -- 2.53.0