From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751052AbeFDR1j (ORCPT ); Mon, 4 Jun 2018 13:27:39 -0400 Received: from mx2.mailbox.org ([80.241.60.215]:37728 "EHLO mx2.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750853AbeFDR1i (ORCPT ); Mon, 4 Jun 2018 13:27:38 -0400 From: Michael Rodin To: tglx@linutronix.de, mingo@redhat.com, x86@kernel.org Cc: hpa@zytor.com, linux-kernel@vger.kernel.org, Michael Rodin Subject: [PATCH] arch/x86/entry/vsyscall/vsyscall_gtod.c: remove __read_mostly from vclocks_used Date: Mon, 4 Jun 2018 19:27:11 +0200 Message-Id: <20180604172711.18962-1-michael-git@rodin.online> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The variable "vclocks_used" doesn't appear to be "read mostly". Measurements of the access frequency with perf stat [1] and perf report show, that approximately half of the accesses to this variable are write accesses and happen in update_vsyscall() in the file arch/x86/entry/vsyscall/vsyscall_gtod.c. The measurements were done with the kernel 4.13.0-43-generic used by ubuntu as well as with the stable kernel 4.16.7 with a custom config. I've used "perf bench sched" and iperf3 as workloads. This was discovered during my master thesis in the CADOS project [2]. [1] perf stat --all-cpus --group --event="{mem:addr/4:rw:k,mem:addr/4:w:k}" [2] https://www.sra.uni-hannover.de/Research/CADOS/ Signed-off-by: Michael Rodin --- arch/x86/entry/vsyscall/vsyscall_gtod.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/entry/vsyscall/vsyscall_gtod.c b/arch/x86/entry/vsyscall/vsyscall_gtod.c index e1216dd95c04..fc39f701fe4a 100644 --- a/arch/x86/entry/vsyscall/vsyscall_gtod.c +++ b/arch/x86/entry/vsyscall/vsyscall_gtod.c @@ -17,7 +17,7 @@ #include #include -int vclocks_used __read_mostly; +int vclocks_used; DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data); -- 2.14.1