From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3AA20C43217 for ; Thu, 1 Dec 2022 11:03:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230117AbiLALDk (ORCPT ); Thu, 1 Dec 2022 06:03:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229631AbiLALDO (ORCPT ); Thu, 1 Dec 2022 06:03:14 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C0B6DA321D for ; Thu, 1 Dec 2022 03:01:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669892488; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dIYgRYjREh+bqtm1hANgqL8y6UtRFdWTjY6cfe7VFrQ=; b=WEQ+qsXr+vDTjMXxUKHsKvSgsr86SDe87QFptvtSry2k6JsirrTs5I8XaoiDmImAIx0wBb ptUTXhZiA2vpNu6282eoNJ9p4xUEH3zXht2Yu+wPKpBKDX9gV0MVGh6L+KCQXLBYhSWtyx AAXm/IFAwmTr/Q0JRNT7Tz8TPLHOkQI= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-306-UBhw5hpiO7qPDmhLau1nMQ-1; Thu, 01 Dec 2022 06:01:27 -0500 X-MC-Unique: UBhw5hpiO7qPDmhLau1nMQ-1 Received: by mail-wr1-f70.google.com with SMTP id g14-20020adfa48e000000b00241f94bcd54so306286wrb.23 for ; Thu, 01 Dec 2022 03:01:27 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=mime-version:message-id:date:references:in-reply-to:subject:cc:to :from:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=dIYgRYjREh+bqtm1hANgqL8y6UtRFdWTjY6cfe7VFrQ=; b=BSlYIMru4paODzlXVK/B1XMuJatJZIlQ502DBPkWaZn44bL3IArbz380LbaoP8Sa9p vqtTluLV0+2ymH81lZiUHD+e4GL3YbHFZmcJRUuPbNAgBILhCfSP9ey0Vn87OU6shsxn Q4FIGm4x6vShBBA+1DGndXdcaszkAIZWXJ/b7/5XnZmQroN+3bWEFRuuw2L2P/yyk54G TReqIn/8HXwBxiUS6+6/0KsQz2C2ivOrhh5eItc0nBNDwhSEoI9A0fKe17r6t8QJf9/S dPe5JjtQQKy1e2+AiiF49b/4ISpKHW7apVCuYkxhS2RMAFpwS8wmvs3/rZ7EaZJw1rIT S5lw== X-Gm-Message-State: ANoB5pnwSxtWGo0wI7TEDvPoaorK+OHwTk/psqHk51Ts6sHZ/S1lo0Dz 9GMEqP9g0cgcTpwbaIn6q4uJ3kZMVVRaz1xEvoSzXvWzwDFj9xU4gPx7tw86ZdJVaTzge0NOg+J GUMeGB6QGKru5L8VslIdBDw0y X-Received: by 2002:a05:6000:1a4e:b0:242:71b:e3cf with SMTP id t14-20020a0560001a4e00b00242071be3cfmr18607703wry.144.1669892486271; Thu, 01 Dec 2022 03:01:26 -0800 (PST) X-Google-Smtp-Source: AA0mqf4nUcVhof4h19m5eYtRbCFNncqAgIXWYD1r7VD9LnwHnEJCDPu/hJHesi7WrnlYjBuoBQFaSg== X-Received: by 2002:a05:6000:1a4e:b0:242:71b:e3cf with SMTP id t14-20020a0560001a4e00b00242071be3cfmr18607680wry.144.1669892486082; Thu, 01 Dec 2022 03:01:26 -0800 (PST) Received: from vschneid.remote.csb ([154.57.232.159]) by smtp.gmail.com with ESMTPSA id p14-20020adf9d8e000000b00236b2804d79sm4148410wre.2.2022.12.01.03.01.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Dec 2022 03:01:25 -0800 (PST) From: Valentin Schneider To: Tejun Heo Cc: linux-kernel@vger.kernel.org, Lai Jiangshan , Peter Zijlstra , Frederic Weisbecker , Juri Lelli , Phil Auld , Marcelo Tosatti Subject: Re: [PATCH v6 3/4] workqueue: Convert the idle_timer to a timer + work_struct In-Reply-To: References: <20221128183109.446754-1-vschneid@redhat.com> <20221128183109.446754-4-vschneid@redhat.com> Date: Thu, 01 Dec 2022 11:01:24 +0000 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/11/22 11:06, Tejun Heo wrote: > On Mon, Nov 28, 2022 at 06:31:08PM +0000, Valentin Schneider wrote: >> @@ -1806,7 +1808,9 @@ static void worker_enter_idle(struct worker *worker) >> /* idle_list is LIFO */ >> list_add(&worker->entry, &pool->idle_list); >> >> - if (too_many_workers(pool) && !timer_pending(&pool->idle_timer)) >> + if (too_many_workers(pool) && >> + !timer_pending(&pool->idle_timer) && >> + !work_pending(&pool->idle_cull_work)) > > Just checking the timer should be enough here, I think. > That would let the timer be re-armed when the cull work is pending, which itself will re-arm the timer to the next non-culled idle worker expiry (if there is any remaining). Not an issue per se, it's just that having the cull work pending is a "promise" that the timer will be re-armed if and when necessary. I think in cases where the cull work doesn't get to run for a while, not having the extra work_pending() check and just arming the timer in worker_enter_idle() might be cheaper than repeatedly checking both timer_pending() and work_pending(), but otherwise I would assume not arming the timer would be preferred. >> mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT); >> >> /* Sanity check nr_running. */ >> @@ -2019,17 +2023,56 @@ static void destroy_worker(struct worker *worker) >> wake_up_process(worker->task); >> } >> >> +/* >> + * idle_worker_timeout - check if some idle workers can now be deleted. > > Might as well turn it into a proper function comment starting w/ "/**" and > with argument list. > Ack. >> + * >> + * The timer is armed in worker_enter_idle(). Note that it isn't disarmed in >> + * worker_leave_idle(), as a worker flicking between idle and active while its >> + * pool is at the too_many_workers() tipping point would cause too much timer >> + * housekeeping overhead. Since IDLE_WORKER_TIMEOUT is long enough, we just let >> + * it expire and re-evaluate things from there. >> + */ >> static void idle_worker_timeout(struct timer_list *t) >> { >> struct worker_pool *pool = from_timer(pool, t, idle_timer); >> + bool do_cull = false; >> + >> + if (work_pending(&pool->idle_cull_work)) >> + return; >> >> raw_spin_lock_irq(&pool->lock); >> >> - while (too_many_workers(pool)) { >> + if (too_many_workers(pool)) { >> struct worker *worker; >> unsigned long expires; >> >> /* idle_list is kept in LIFO order, check the last one */ >> + worker = list_entry(pool->idle_list.prev, struct worker, entry); >> + expires = worker->last_active + IDLE_WORKER_TIMEOUT; >> + do_cull = !time_before(jiffies, expires); >> + >> + if (!do_cull) >> + mod_timer(&pool->idle_timer, expires); >> + } >> + raw_spin_unlock_irq(&pool->lock); >> + >> + if (do_cull) >> + queue_work(system_unbound_wq, &pool->idle_cull_work); >> +} >> + >> +/* >> + * idle_cull_fn - cull workers that have been idle for too long. >> + */ > > Please turn it into a full function comment or drop the wings (ie. make it > an one-liner). > Patch 4/4 adds the rest of the comment, but I can make the whole thing appear in patch 4 if you prefer.