From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-we0-f172.google.com ([74.125.82.172]:46263 "EHLO mail-we0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753922Ab3KWQai (ORCPT ); Sat, 23 Nov 2013 11:30:38 -0500 Received: by mail-we0-f172.google.com with SMTP id t60so2336474wes.3 for ; Sat, 23 Nov 2013 08:30:37 -0800 (PST) Message-ID: <5290D826.5080308@gmail.com> Date: Sat, 23 Nov 2013 17:30:30 +0100 From: Sylwester Nawrocki MIME-Version: 1.0 To: Hans Verkuil , Wade Farnsworth CC: linux-media@vger.kernel.org, m.chehab@samsung.com Subject: Re: [PATCH] v4l2-dev: Add tracepoints for QBUF and DQBUF References: <52614DB9.8090908@mentor.com> <528FB50C.6060909@mentor.com> <529090A9.7030505@xs4all.nl> In-Reply-To: <529090A9.7030505@xs4all.nl> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hi, On 11/23/2013 12:25 PM, Hans Verkuil wrote: > Hi Wade, > > On 11/22/2013 08:48 PM, Wade Farnsworth wrote: >> Add tracepoints to the QBUF and DQBUF ioctls to enable rudimentary >> performance measurements using standard kernel tracers. >> >> Signed-off-by: Wade Farnsworth >> --- >> >> This is the update to the RFC patch I posted a few weeks back. I've added >> several bits of metadata to the tracepoint output per Mauro's suggestion. > > I don't like this. All v4l2 ioctls can already be traced by doing e.g. > echo 1 (or echo 2)>/sys/class/video4linux/video0/debug. > > So this code basically duplicates that functionality. It would be nice to be able > to tie in the existing tracing code (v4l2-ioctl.c) into tracepoints. I think it would be really nice to have this kind of support for standard traces at the v4l2 subsystem. Presumably it could even gradually replace the v4l2 custom debug infrastructure. If I understand things correctly, the current tracing/profiling infrastructure is much less invasive than inserting printks all over, which may cause changes in control flow. I doubt the system could be reliably profiled by enabling all those debug prints. So my vote would be to add support for standard tracers, like in other subsystems in the kernel. -- Regards, Sylwester