From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (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 EC7361A34CA for ; Fri, 2 Aug 2024 16:06:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722614804; cv=none; b=SxnchKxTyV5VEF0crERS7DXWfMUTa5AivND9Dax0DnzAQRC2dv+FPbJglFes4b26Mj9YJA9E9EJPswQyA15PlwkeSEPBIuhObhsUZECsmtDRpRmLsSZTuVpGLQNfiBh0I/h79ufR/jAOzCXvaqO5AKh66L27vYMctjSnW2fyNz0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722614804; c=relaxed/simple; bh=BBL1nzxq3HA9H2ov3xyYeuHlmDlYV3KxeNa9ypWkDVM=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=e8AGoWxyaqHOnM/GOQ9U2dEbH9Jrnm5jBZxUW4olwG1TkIV17nUzVJTC0coPE68wXgtZPiR6kZS/i+J6KVBZ+DBA30mVEcUXqB/6qh6VigTt8CQalsKQ9otUMdk+ImRNqOin6gSBWwpyyixXRqkuXXUerVyY1zeJjxnPBmenNa0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=shelob.surriel.com; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=shelob.surriel.com Received: from [2601:18c:9101:a8b6:6e0b:84ff:fee2:98bb] (helo=imladris.surriel.com) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1sZun9-000000006w9-052N; Fri, 02 Aug 2024 12:06:07 -0400 Message-ID: Subject: Re: [PATCH misc 1/2] workqueue: Add check for clocks going backwards to wq_worker_tick() From: Rik van Riel To: "Paul E. McKenney" , linux-kernel@vger.kernel.org Cc: Tejun Heo , Lai Jiangshan , Breno Leitao , Anhad Jai Singh , Oleg Nesterov , Jens Axboe , Christian Brauner , Andrew Morton , "Matthew Wilcox (Oracle)" , Chris Mason Date: Fri, 02 Aug 2024 12:06:06 -0400 In-Reply-To: <20240802003046.4134043-1-paulmck@kernel.org> References: <20240802003046.4134043-1-paulmck@kernel.org> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Sender: riel@surriel.com On Thu, 2024-08-01 at 17:30 -0700, Paul E. McKenney wrote: >=20 > +++ b/kernel/workqueue.c > @@ -1482,6 +1482,7 @@ void wq_worker_tick(struct task_struct *task) > =C2=A0 * If the current worker is concurrency managed and hogged > the CPU for > =C2=A0 * longer than wq_cpu_intensive_thresh_us, it's > automatically marked > =C2=A0 * CPU_INTENSIVE to avoid stalling other concurrency-managed > work items. > + * If the time is negative, ignore, assuming a backwards > clock. > =C2=A0 * > =C2=A0 * Set @worker->sleeping means that @worker is in the > process of > =C2=A0 * switching out voluntarily and won't be contributing to > @@ -1491,6 +1492,7 @@ void wq_worker_tick(struct task_struct *task) > =C2=A0 * We probably want to make this prettier in the future. > =C2=A0 */ > =C2=A0 if ((worker->flags & WORKER_NOT_RUNNING) || > READ_ONCE(worker->sleeping) || > + =C2=A0=C2=A0=C2=A0 WARN_ON_ONCE((s64)(worker->task->se.sum_exec_runtime= - > worker->current_at) < 0) || > =C2=A0 =C2=A0=C2=A0=C2=A0 worker->task->se.sum_exec_runtime - worker->cur= rent_at < > =C2=A0 =C2=A0=C2=A0=C2=A0 wq_cpu_intensive_thresh_us * NSEC_PER_USEC) > =C2=A0 return; What is the code path by which sum_exec_runtime could go backward in time, if the TSC and sched_clock() jump backward? Might it make sense to check in the place where sum_exec_runtime is updated, instead, and catch a wider net? On the flip side, the run time increments are "fairly large" in number of TSC cycles, while most of the negative TSC jumps we=C2=A0 have seen are quite small, so even that wider net might not catch much because of how coarse these updates typically are... --=20 All Rights Reversed.