Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752376AbcJUEiL (ORCPT ); Fri, 21 Oct 2016 00:38:11 -0400 Received: from mail-it0-f67.google.com ([209.85.214.67]:36242 "EHLO mail-it0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751164AbcJUEiI (ORCPT ); Fri, 21 Oct 2016 00:38:08 -0400 From: Vince Weaver X-Google-Original-From: Vince Weaver Date: Fri, 21 Oct 2016 00:38:06 -0400 (EDT) X-X-Sender: vince@macbook-air To: "Michael Kerrisk (man-pages)" cc: linux-man@vger.kernel.org, linux-kernel@vger.kernel.org, Adrian Hunter , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo Subject: [patch] perf_event_open.2: update time_shift sample code 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: 1308 Lines: 37 Linux 4.3 (b20112edeadf0b8a1416de061caa4beb11539902) improved the accuracy of the clock/ns conversion routines. As a result the shift factor can now be 32. This value is directly exported in the perf_event_open() mmap page, and this potentially breaks the sample code that shifts 1 left by the shift value. Add a cast in the sample code so that a proper 64-bit value results from the shift. This is the same change that was made to the sample code in include/uapi/linux/perf_event.h in Linux 4.4 (b9511cd761faafca7a1acc059e792c1399f9d7c6). Signed-off-by: Vince Weaver diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2 index ae15cc6..fade28c 100644 --- a/man2/perf_event_open.2 +++ b/man2/perf_event_open.2 @@ -1619,7 +1619,7 @@ delta since u64 quot, rem; u64 delta; quot = (cyc >> time_shift); - rem = cyc & ((1 << time_shift) \- 1); + rem = cyc & (((u64)1 << time_shift) \- 1); delta = time_offset + quot * time_mult + ((rem * time_mult) >> time_shift); .fi @@ -1664,7 +1664,7 @@ And vice versa: .nf quot = cyc >> time_shift; - rem = cyc & ((1 << time_shift) - 1); + rem = cyc & (((u64)1 << time_shift) - 1); timestamp = time_zero + quot * time_mult + ((rem * time_mult) >> time_shift); .fi