Date: Sat, 25 Jul 2020 07:14:33 +0000 (UTC) From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r363511 - head/sys/kern Message-ID: <202007250714.06P7EXHu016497@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
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); }
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?202007250714.06P7EXHu016497>