From owner-svn-src-head@freebsd.org Sat Jul 25 07:14:34 2020 Return-Path: Delivered-To: svn-src-head@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 42BC93A1DB8; Sat, 25 Jul 2020 07:14:34 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4BDHPk12fmz3b8y; Sat, 25 Jul 2020 07:14:34 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 07AF918015; Sat, 25 Jul 2020 07:14:34 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 06P7EX5G016498; Sat, 25 Jul 2020 07:14:33 GMT (envelope-from mjg@FreeBSD.org) Received: (from mjg@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 06P7EXHu016497; Sat, 25 Jul 2020 07:14:33 GMT (envelope-from mjg@FreeBSD.org) Message-Id: <202007250714.06P7EXHu016497@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: mjg set sender to mjg@FreeBSD.org using -f From: Mateusz Guzik Date: Sat, 25 Jul 2020 07:14:33 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r363511 - head/sys/kern X-SVN-Group: head X-SVN-Commit-Author: mjg X-SVN-Commit-Paths: head/sys/kern X-SVN-Commit-Revision: 363511 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 25 Jul 2020 07:14:34 -0000 Author: mjg Date: Sat Jul 25 07:14:33 2020 New Revision: 363511 URL: https://svnweb.freebsd.org/changeset/base/363511 Log: Do a lockless check in kthread_suspend_check Otherwise an idle system running lockstat sleep 10 reports contention on process lock comming from bufdaemon. While here fix a style nit. Modified: head/sys/kern/kern_kthread.c Modified: head/sys/kern/kern_kthread.c ============================================================================== --- head/sys/kern/kern_kthread.c Sat Jul 25 06:32:23 2020 (r363510) +++ head/sys/kern/kern_kthread.c Sat Jul 25 07:14:33 2020 (r363511) @@ -441,12 +441,15 @@ kthread_suspend_check(void) panic("%s: curthread is not a valid kthread", __func__); /* - * As long as the double-lock protection is used when accessing the - * TDF_KTH_SUSP flag, synchronizing the read operation via proc mutex - * is fine. + * Setting the TDF_KTH_SUSP flag is protected by process lock. + * + * Do an unlocked read first to avoid serializing with all other threads + * in the common case of not suspending. */ + if ((td->td_flags & TDF_KTH_SUSP) == 0) + return; PROC_LOCK(p); - while (td->td_flags & TDF_KTH_SUSP) { + while ((td->td_flags & TDF_KTH_SUSP) != 0) { wakeup(&td->td_flags); msleep(&td->td_flags, &p->p_mtx, PPAUSE, "ktsusp", 0); }