From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) (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 A1A77363C79 for ; Fri, 24 Jul 2026 04:12:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784866327; cv=none; b=nV32695LY+OWERtsOF0W5CK/fBfVymB9SrJgw2Lhx0P8pcHzeARZ/giNZqsCraxvHK0YEg5zV2cz4UGouP550Yxs3WaUf51auSxrUGi1mh+B7Ttt8Wx65LIa/x7hlWo/KT5nVl3533Iwfpj/OV4+voeXybXI6WNMa09zU53LVXI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784866327; c=relaxed/simple; bh=9gUGwdJQriG9BhAwKkvxj4R4ihga2c7bsLePSYw7Bv4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RMfETHLz9s2/0ScjJbzFASv9uP+GQobdM3QFFe+WdaJQIC0b858UvEeYthK0TVqpk6NzyjMJKrBDH/1vqI1S/56yL/K3Agw1wfgC3hr3f3o0YvmLeV1LeHblkbGLe0P+7UMLq9awGwgS8g8tO3DMD8ts/KGYqMn3wiRTuhUDuDQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=omZh9vUV; arc=none smtp.client-ip=91.218.175.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="omZh9vUV" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784866323; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ckmJRpP0nZ2gtB6gT9YYriokoaTnVsOuxWDjymqwiGw=; b=omZh9vUVg1B1udU8FgYcVoVa8rZrRWcY6eolqNtwv2kZhWsk3sJLFMGXqfSGwNuiGBjo9Q eDMYYjCQfb9awZeY9TiI7o5VmfTr8RSQZEaaxN0NzDi06LLQ/9gsLU/AfOC662Jg2bgHVx HkhKNDfKRD96vnFmS9XU/pgtVSdrKsM= From: Tao Cui To: Johannes Weiner , Suren Baghdasaryan Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Tao Cui , cui.tao@linux.dev Subject: [PATCH 1/2] sched/psi: fix trigger window growth interpolation for large windows Date: Fri, 24 Jul 2026 12:11:45 +0800 Message-ID: <20260724041146.510027-2-cui.tao@linux.dev> In-Reply-To: <20260724041146.510027-1-cui.tao@linux.dev> References: <20260724041146.510027-1-cui.tao@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Tao Cui window_update() estimates the stall growth inside a partially elapsed trigger window as growth += win->prev_growth * remaining / win->size with `remaining = win->size - elapsed`. The local `remaining` is a u32, but win->size is a u64 and may be as large as WINDOW_MAX_US (10s = 10^10 ns), which exceeds UINT32_MAX (~4.29s). For trigger windows larger than ~4.29s the assignment truncates `remaining`, the linear interpolation collapses, and growth is heavily underestimated. For a 10s window polled once per second with prev_growth equal to a full window of stall, the estimate one second in is ~1.4s instead of 10s. A trigger configured as "some 5s 10s" then waits until the actual stall reaches the threshold (~4s in) instead of firing as soon as the run-rate predicts it (~1s in): a multi-second delay on the first window of a stall. Use a u64 `remaining` and mul_u64_u64_div_u64() for the product, which also avoids the u64 overflow of `prev_growth * remaining` under heavy pressure. This runs in update_triggers() at trigger-evaluation rate (at most a few times per second), not the scheduler hot path, so the helper's cost is immaterial. Fixes: 0e94682b73bf ("psi: introduce psi monitor") Signed-off-by: Tao Cui --- kernel/sched/psi.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 4e152410653d..6514b44222cf 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -451,10 +451,11 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value) if (elapsed > win->size) window_reset(win, now, value, growth); else { - u32 remaining; + u64 remaining; remaining = win->size - elapsed; - growth += div64_u64(win->prev_growth * remaining, win->size); + growth += mul_u64_u64_div_u64(win->prev_growth, remaining, + win->size); } return growth; -- 2.43.0