From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751733AbeCXIJy (ORCPT ); Sat, 24 Mar 2018 04:09:54 -0400 Received: from mail-wr0-f176.google.com ([209.85.128.176]:41661 "EHLO mail-wr0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750797AbeCXIJu (ORCPT ); Sat, 24 Mar 2018 04:09:50 -0400 X-Google-Smtp-Source: AG47ELsjn6Ji/+ONxbFMelf8yIGx5P4FYHMdQKEHJBNqiQYMY1G/83yXw2wgDEtpyDwMYaCSYW/85Q== Date: Sat, 24 Mar 2018 09:09:46 +0100 From: Ingo Molnar To: Eric Dumazet Cc: x86 , lkml , Eric Dumazet , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Hugh Dickins , Peter Zijlstra Subject: Re: [PATCH v3 1/2] x86, msr: allow rdmsr_safe_on_cpu() to schedule Message-ID: <20180324080946.3db4xdkl5i6jx2rc@gmail.com> References: <20180323215818.127774-1-edumazet@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180323215818.127774-1-edumazet@google.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Eric Dumazet wrote: > I noticed high latencies caused by a daemon periodically reading > various MSR on all cpus. KASAN kernels would see ~10ms latencies > simply reading one MSR. Even without KASAN, sending IPI to CPU > in deep sleep state or blocking hard IRQ in a a long section, > then waiting for the answer can consume hundreds of usec. > > Converts rdmsr_safe_on_cpu() to use a completion instead > of busy polling. > > Overall daemon cpu usage was reduced by 35 %, > and latencies caused by msr_read() disappeared. What "daemon" is this and why is it reading MSRs? Thanks, Ingo