Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755009AbdCPPzv (ORCPT ); Thu, 16 Mar 2017 11:55:51 -0400 Received: from mail-it0-f67.google.com ([209.85.214.67]:34456 "EHLO mail-it0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754577AbdCPPzr (ORCPT ); Thu, 16 Mar 2017 11:55:47 -0400 From: Vince Weaver X-Google-Original-From: Vince Weaver Date: Thu, 16 Mar 2017 11:54:58 -0400 (EDT) X-X-Sender: vince@macbook-air To: linux-kernel@vger.kernel.org cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo Subject: perf: massive perf_event slowdown between 4.9 and 4.11-rc Message-ID: User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 920 Lines: 36 Hello My student actually noticed this before I did, I was hoping it was some sort of error in her data. Anyway all perf_event functionality (especially reads) has become about 20x slower, at least on Intel machines (haswell and skylake are the only ones I've tested) sometime between 4.9 and 4.11-rc For example, in the PAPI tests: 4.11-rc2 Total cost for PAPI_read (2 counters) over 1000000 iterations min cycles : 15192 max cycles : 3887735 mean cycles : 15662.057418 std deviation: 19079.398693 4.9 Total cost for PAPI_read (2 counters) over 1000000 iterations min cycles : 864 max cycles : 78459 mean cycles : 908.010315 std deviation: 144.875697 The perf_event_test validation tests are also showing this, even when using rdpmc() rather than read. Is there a likely change that might have caused this? Hoping to avoid bisecting it as that will kill the rest of the week probably. Vince