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: Wed, 29 Jun 2011 19:25:58 +0300 Message-ID: <4E0B5216.4060403@redhat.com> References: <1309362157-6596-1-git-send-email-avi@redhat.com> <1309362157-6596-2-git-send-email-avi@redhat.com> <20110629160841.GA2032@somewhere> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Ingo Molnar , a.p.zijlstra@chello.nl, acme@ghostprotocols.net, Will Deacon , Jason Wessel To: Frederic Weisbecker Return-path: In-Reply-To: <20110629160841.GA2032@somewhere> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 06/29/2011 07:08 PM, Frederic Weisbecker wrote: > On Wed, Jun 29, 2011 at 06:42:35PM +0300, Avi Kivity wrote: > > The perf_event overflow handler does not receive any caller-derived > > argument, so many callers need to resort to looking up the perf_event > > in their local data structure. This is ugly and doesn't scale if a > > single callback services many perf_events. > > > > Fix by adding a context parameter to perf_event_create_kernel_counter() > > (and derived hardware breakpoints APIs) and storing it in the perf_event. > > The field can be accessed from the callback as event->overflow_handler_context. > > All callers are updated. > > > > Signed-off-by: Avi Kivity > > I believe it can micro-optimize ptrace through register_user_hw_breakpoint() because > we could store the index of the breakpoint that way, instead of iterating through 4 slots. > Right, I noticed that while writing the patch. > Perhaps it can help in arm too, adding Will in Cc. > > But for register_wide_hw_breakpoint, I'm not sure. kgdb is the main user, may be Jason > could find some use of it. I think an API should not require its users to iterate in their callbacks, even if it doesn't affect current users for some reason. -- error compiling committee.c: too many arguments to function