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 5CBF517DC1B; Sun, 24 Mar 2024 23:44:02 +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=1711323843; cv=none; b=tjephUuUNGcdVnlq/xIdJN7Ka/7Xg70nSzO4wQM35jX40Af22nVpVLXqhR91EZGyrkdHRazbaCw2DZl3F+Qu8O8ADFxM0X72S0lmIIZJH2uTUAFcfBhETe6vlWVcv1xzzgjJZ8lJ10isWqa2afFwor7oVFuukZEQ1RMdjzWI410= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711323843; c=relaxed/simple; bh=W0aSp3rIAkXDSRRDV929dU0asFR/emNu7jE6ME/72Rg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OCNoB1mljkFlIPf1aVC+ZwvupRhYmNpNluonKp9IV3ehTRHbAOEubMK1T2eJ83lUdTe/hOPAyGEkqjFADhao4eW5JZLfUuZ6HTjlmqzgbl1I3WprrhJztBOafxrJI20lA7JhJibpLq+TuCicRtj1Qe27yyCvCoTMuv9CrwSMoPc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XZmug1Yh; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XZmug1Yh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 83286C433C7; Sun, 24 Mar 2024 23:44:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711323842; bh=W0aSp3rIAkXDSRRDV929dU0asFR/emNu7jE6ME/72Rg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XZmug1YheXygnwAz2OCGJhBVsG6JEht3hNAT2MGfnXU97vS8lPJLuXjLecn6TODFz wpr6/Y5V0YO9RIg5hU9LRdGGZ105sIweBzwPQexk1Y1h/1hCYba+vufUQNgDkJtJAr JOimnxoUNdGxGZS4dU7jh0k4Qs4LyZdCCep3uEgRRKQh2G/DHRzrPYYLQDEqhozx68 HidtzHs8mCT152HTUynC1ZoTA9PKYZI2IA3D9qSjF8D1lrNynB39aTLxvcVujiCrey ExpNt4w79sLmqZMwnSr0Xc1HEQFgbTfaHaqnbEZgW+XHE16kZ3HYcrIwjwYr0nKakp ri7I4ip/78Uyw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Mete Durlu , Heiko Carstens , Christian Borntraeger , Sasha Levin Subject: [PATCH 5.10 220/238] s390/vtime: fix average steal time calculation Date: Sun, 24 Mar 2024 19:40:08 -0400 Message-ID: <20240324234027.1354210-221-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240324234027.1354210-1-sashal@kernel.org> References: <20240324234027.1354210-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit From: Mete Durlu [ Upstream commit 367c50f78451d3bd7ad70bc5c89f9ba6dec46ca9 ] Current average steal timer calculation produces volatile and inflated values. The only user of this value is KVM so far and it uses that to decide whether or not to yield the vCPU which is seeing steal time. KVM compares average steal timer to a threshold and if the threshold is past then it does not allow CPU polling and yields it to host, else it keeps the CPU by polling. Since KVM's steal time threshold is very low by default (%10) it most likely is not effected much by the bloated average steal timer values because the operating region is pretty small. However there might be new users in the future who might rely on this number. Fix average steal timer calculation by changing the formula from: avg_steal_timer = avg_steal_timer / 2 + steal_timer; to the following: avg_steal_timer = (avg_steal_timer + steal_timer) / 2; This ensures that avg_steal_timer is actually a naive average of steal timer values. It now closely follows steal timer values but of course in a smoother manner. Fixes: 152e9b8676c6 ("s390/vtime: steal time exponential moving average") Signed-off-by: Mete Durlu Acked-by: Heiko Carstens Acked-by: Christian Borntraeger Signed-off-by: Heiko Carstens Signed-off-by: Sasha Levin --- arch/s390/kernel/vtime.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c index 579ec3a8c816f..bd65ff88c5baa 100644 --- a/arch/s390/kernel/vtime.c +++ b/arch/s390/kernel/vtime.c @@ -214,13 +214,13 @@ void vtime_flush(struct task_struct *tsk) virt_timer_expire(); steal = S390_lowcore.steal_timer; - avg_steal = S390_lowcore.avg_steal_timer / 2; + avg_steal = S390_lowcore.avg_steal_timer; if ((s64) steal > 0) { S390_lowcore.steal_timer = 0; account_steal_time(cputime_to_nsecs(steal)); avg_steal += steal; } - S390_lowcore.avg_steal_timer = avg_steal; + S390_lowcore.avg_steal_timer = avg_steal / 2; } /* -- 2.43.0