Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758401Ab1FPOqh (ORCPT ); Thu, 16 Jun 2011 10:46:37 -0400 Received: from li9-11.members.linode.com ([67.18.176.11]:59605 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758311Ab1FPOqg (ORCPT ); Thu, 16 Jun 2011 10:46:36 -0400 Date: Thu, 16 Jun 2011 10:46:26 -0400 Message-Id: To: linux-kernel@vger.kernel.org Subject: scheduler / perf stat question about CPU-migrations From: "Theodore Ts'o" Phone: (781) 391-3464 X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on test.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1669 Lines: 41 Can someone tell me how I'm being confused? I ran the following command as root: perf stat schedtool -a 1 -e e2fsck -ft /dev/funarg/kbuild This runs e2fsck under perf, with the cpu affinity nailed to a single CPU. I therefore expected the CPU-migrations field reported by perf to be 0. That was not what I found, though: Performance counter stats for 'schedtool -a 1 -e e2fsck -ft /dev/funarg/kbuild': 1169.715766 task-clock-msecs # 0.180 CPUs 9212 context-switches # 0.008 M/sec 307 CPU-migrations # 0.000 M/sec 1875 page-faults # 0.002 M/sec 2737168498 cycles # 2340.029 M/sec 3125632038 instructions # 1.142 IPC 688556730 branches # 588.653 M/sec 7263580 branch-misses # 1.055 % 15222417 cache-references # 13.014 M/sec 1488633 cache-misses # 1.273 M/sec 6.481483548 seconds time elapsed How could this be? The CPU-migrations event counter only gets incremented if a task changes CPU's, as seen in kernel/sched.c: if (task_cpu(p) != new_cpu) { p->se.nr_migrations++; perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 1, NULL, 0); } So it should be 0, not 307, right? What am I missing? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/