From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 1/3] perf: add context field to perf_event Date: Tue, 12 Jul 2011 13:07:25 +0300 Message-ID: <4E1C1CDD.9040005@redhat.com> References: <4E1C0F02.9040906@redhat.com> <1310462046.14978.11.camel@twins> <4E1C10F8.6010300@redhat.com> <1310462335.14978.12.camel@twins> <4E1C1373.5080500@redhat.com> <1310463060.14978.17.camel@twins> <20110712094131.GA29812@8bytes.org> <4E1C1771.9010300@redhat.com> <20110712094822.GB29812@8bytes.org> <4E1C1A0D.8000707@redhat.com> <20110712100354.GC29812@8bytes.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , Will Deacon , Frederic Weisbecker , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , Ingo Molnar , "acme@ghostprotocols.net" , Jason Wessel To: Joerg Roedel Return-path: In-Reply-To: <20110712100354.GC29812@8bytes.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 07/12/2011 01:03 PM, Joerg Roedel wrote: > > Regarding LWP - I thought the intent was self-profiling by the process > > for jits and the like? If you also use it for perf, won't it be > > unusable for that? Also, can't the process interfere, from userspace, > > by executing the unprivileged LWP instructions? > > Ingo made perf-integration a merge-requirement for LWP. It is not really > well-suited for being integrated into perf because the design goal was > easy and efficient self-profiling of tasks (like you stated). So > integrating it into perf causes some pain. But lets see how it works > out. I don't think it's workable. Having do_mmap() called in the task's context can change how it works. And the task being able to kill/modify the profile, and not able to use LWP for itself, is a show stopper IMO. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.