From owner-svn-src-stable-9@FreeBSD.ORG Mon Jul 30 15:30:43 2012 Return-Path: Delivered-To: svn-src-stable-9@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id F1FAA1065734; Mon, 30 Jul 2012 15:30:42 +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 DABC18FC0A; Mon, 30 Jul 2012 15:30:42 +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 q6UFUgTX007348; Mon, 30 Jul 2012 15:30:42 GMT (envelope-from jimharris@svn.freebsd.org) Received: (from jimharris@localhost) by svn.freebsd.org (8.14.4/8.14.4/Submit) id q6UFUgkb007346; Mon, 30 Jul 2012 15:30:42 GMT (envelope-from jimharris@svn.freebsd.org) Message-Id: <201207301530.q6UFUgkb007346@svn.freebsd.org> From: Jim Harris Date: Mon, 30 Jul 2012 15:30:42 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org X-SVN-Group: stable-9 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: Subject: svn commit: r238910 - stable/9/sys/x86/x86 X-BeenThere: svn-src-stable-9@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for only the 9-stable src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 30 Jul 2012 15:30:43 -0000 Author: jimharris Date: Mon Jul 30 15:30:42 2012 New Revision: 238910 URL: http://svn.freebsd.org/changeset/base/238910 Log: MFC r238755: 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 Approved by: re (kib) Modified: stable/9/sys/x86/x86/tsc.c Directory Properties: stable/9/sys/ (props changed) Modified: stable/9/sys/x86/x86/tsc.c ============================================================================== --- stable/9/sys/x86/x86/tsc.c Mon Jul 30 14:47:35 2012 (r238909) +++ stable/9/sys/x86/x86/tsc.c Mon Jul 30 15:30:42 2012 (r238910) @@ -326,6 +326,7 @@ 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) \ @@ -333,6 +334,7 @@ tsc_read_##x(void *arg) \ uint32_t *tsc = arg; \ u_int cpu = PCPU_GET(cpuid); \ \ + rmb(); \ tsc[cpu * 3 + x] = rdtsc32(); \ } TSC_READ(0)