From owner-svn-src-all@FreeBSD.ORG Tue Jul 24 22:10:12 2012 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7BF49106566B; Tue, 24 Jul 2012 22:10:12 +0000 (UTC) (envelope-from jimharris@FreeBSD.org) Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:4f8:fff6::2c]) by mx1.freebsd.org (Postfix) with ESMTP id 66F608FC16; Tue, 24 Jul 2012 22:10:12 +0000 (UTC) Received: from svn.freebsd.org (localhost [127.0.0.1]) by svn.freebsd.org (8.14.4/8.14.4) with ESMTP id q6OMACQR079605; Tue, 24 Jul 2012 22:10:12 GMT (envelope-from jimharris@svn.freebsd.org) Received: (from jimharris@localhost) by svn.freebsd.org (8.14.4/8.14.4/Submit) id q6OMACqV079603; Tue, 24 Jul 2012 22:10:12 GMT (envelope-from jimharris@svn.freebsd.org) Message-Id: <201207242210.q6OMACqV079603@svn.freebsd.org> From: Jim Harris Date: Tue, 24 Jul 2012 22:10:12 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org X-SVN-Group: head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: Subject: svn commit: r238755 - head/sys/x86/x86 X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 24 Jul 2012 22:10:12 -0000 Author: jimharris Date: Tue Jul 24 22:10:11 2012 New Revision: 238755 URL: http://svn.freebsd.org/changeset/base/238755 Log: Add rmb() to tsc_read_##x to enforce serialization of rdtsc captures. Intel Architecture Manual specifies that rdtsc instruction is not serialized, so without this change, TSC synchronization test would periodically fail, resulting in use of HPET timecounter instead of TSC-low. This caused severe performance degradation (40-50%) when running high IO/s workloads due to HPET MMIO reads and GEOM stat collection. Tests on Xeon E5-2600 (Sandy Bridge) 8C systems were seeing TSC synchronization fail approximately 20% of the time. Sponsored by: Intel Reviewed by: kib MFC after: 3 days Modified: head/sys/x86/x86/tsc.c Modified: head/sys/x86/x86/tsc.c ============================================================================== --- head/sys/x86/x86/tsc.c Tue Jul 24 20:15:41 2012 (r238754) +++ head/sys/x86/x86/tsc.c Tue Jul 24 22:10:11 2012 (r238755) @@ -328,6 +328,7 @@ init_TSC(void) #ifdef SMP +/* rmb is required here because rdtsc is not a serializing instruction. */ #define TSC_READ(x) \ static void \ tsc_read_##x(void *arg) \ @@ -335,6 +336,7 @@ tsc_read_##x(void *arg) \ uint32_t *tsc = arg; \ u_int cpu = PCPU_GET(cpuid); \ \ + rmb(); \ tsc[cpu * 3 + x] = rdtsc32(); \ } TSC_READ(0)