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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7BA5C43441 for ; Tue, 13 Nov 2018 16:34:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AEB9B223DD for ; Tue, 13 Nov 2018 16:34:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CXKh9szP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AEB9B223DD Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731286AbeKNCcz (ORCPT ); Tue, 13 Nov 2018 21:32:55 -0500 Received: from mail-qk1-f196.google.com ([209.85.222.196]:43133 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727475AbeKNCcz (ORCPT ); Tue, 13 Nov 2018 21:32:55 -0500 Received: by mail-qk1-f196.google.com with SMTP id r71so20432573qkr.10; Tue, 13 Nov 2018 08:34:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=jR0fRYp/BIYNsG6MN55gk0oGE8HOfcc6D5XxTxN3+DE=; b=CXKh9szPa8YSyGfC/4hyGn5tcixv/PpE23S3bQovGvWKSyguU74qTR2KVMf8bqbnmf ae6f7apxPzksUZIcwgKLkWLZUpasR1HJpwGVsBczWMDGFzz8pS2pswprAJIlLL5///pv RNQH2FWliPuFtvhd8Z6p0wfFzu3EWyvSUGGYa8dYSH1m8R8IZi3J+zTT7Q/XIkgm/hJe 8ylN7kuotKbXKrgCOjFbdWcplqph16J4+Rho52Uecq7wIeNwXHRp9gZldbDBMETTUYEN 1tHIxvK0X2chQfK8s1NhfImlU0Ktwbi88k9K92KEswJgQKhP42sLAXp+xuLhGiSuXVr9 gysg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=jR0fRYp/BIYNsG6MN55gk0oGE8HOfcc6D5XxTxN3+DE=; b=lTFDOwLvoTf6z4IpbqV6krkLvhgkMTkPtZ+hVDEse3ZfrMlP/AMslHV8hI4agY5W5t PaRrOECoz1B+CsA1RIczMq+ZTe8uGof0UAcyJWcSU3gPutDngn11L1fJrkTuCc4hGDEG uNjocsZe330kRv/me4ai7wwGoe8kHTXqBaoKisUDlLXmD6EYigi3xKQEIfOnBhTur/+i LddppfEaPQwtddNjQH+xdYwiKOUitKj8uwFg8phkGWFmst5hlts7t2UGnCJPjJzSslQs MWvuQWb6N1PYqoaflo8KWRXPNAEugjyzT8+KPjinNTALY6SXkXmNO54AUSixgWXVBirJ AP/w== X-Gm-Message-State: AGRZ1gLxqHq1chhQN6hgcYqjdp+SaLRulJu+/tEIwRbFYk4RiZkI7Uxl VG9sgZbNhY713zEVXfvpWs8= X-Google-Smtp-Source: AJdET5dMTIEfKWQKZI/WU6auRQ6dGL0V06VujjT7g5/5XsWakvJ9zgmOb9z9SllulweVIw9LFlEbVQ== X-Received: by 2002:a37:24c9:: with SMTP id k70mr5544517qkk.281.1542126844139; Tue, 13 Nov 2018 08:34:04 -0800 (PST) Received: from localhost ([2620:10d:c091:200::6:e2a7]) by smtp.gmail.com with ESMTPSA id y14sm14295842qky.83.2018.11.13.08.34.02 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 13 Nov 2018 08:34:03 -0800 (PST) Date: Tue, 13 Nov 2018 08:34:00 -0800 From: Tejun Heo To: Daniel Jordan Cc: linux-mm@kvack.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, aarcange@redhat.com, aaron.lu@intel.com, akpm@linux-foundation.org, alex.williamson@redhat.com, bsd@redhat.com, darrick.wong@oracle.com, dave.hansen@linux.intel.com, jgg@mellanox.com, jwadams@google.com, jiangshanlai@gmail.com, mhocko@kernel.org, mike.kravetz@oracle.com, Pavel.Tatashin@microsoft.com, prasad.singamsetty@oracle.com, rdunlap@infradead.org, steven.sistare@oracle.com, tim.c.chen@intel.com, vbabka@suse.cz Subject: Re: [RFC PATCH v4 05/13] workqueue, ktask: renice helper threads to prevent starvation Message-ID: <20181113163400.GK2509588@devbig004.ftw2.facebook.com> References: <20181105165558.11698-1-daniel.m.jordan@oracle.com> <20181105165558.11698-6-daniel.m.jordan@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181105165558.11698-6-daniel.m.jordan@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Daniel. On Mon, Nov 05, 2018 at 11:55:50AM -0500, Daniel Jordan wrote: > static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr, > - bool from_cancel) > + struct nice_work *nice_work, int flags) > { > struct worker *worker = NULL; > struct worker_pool *pool; > @@ -2868,11 +2926,19 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr, > if (pwq) { > if (unlikely(pwq->pool != pool)) > goto already_gone; > + > + /* not yet started, insert linked work before work */ > + if (unlikely(flags & WORK_FLUSH_AT_NICE)) > + insert_nice_work(pwq, nice_work, work); So, I'm not sure this works that well. e.g. what if the work item is waiting for other work items which are at lower priority? Also, in this case, it'd be a lot simpler to simply dequeue the work item and execute it synchronously. > } else { > worker = find_worker_executing_work(pool, work); > if (!worker) > goto already_gone; > pwq = worker->current_pwq; > + if (unlikely(flags & WORK_FLUSH_AT_NICE)) { > + set_user_nice(worker->task, nice_work->nice); > + worker->flags |= WORKER_NICED; > + } > } I'm not sure about this. Can you see whether canceling & executing synchronously is enough to address the latency regression? Thanks. -- tejun