From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753247AbaIXHtt (ORCPT ); Wed, 24 Sep 2014 03:49:49 -0400 Received: from mail-we0-f181.google.com ([74.125.82.181]:50931 "EHLO mail-we0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752982AbaIXHtr (ORCPT ); Wed, 24 Sep 2014 03:49:47 -0400 Date: Wed, 24 Sep 2014 09:49:42 +0200 From: Ingo Molnar To: Pawel Moll Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Richard Cochran , Steven Rostedt , Peter Zijlstra , Paul Mackerras , John Stultz , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" Subject: Re: [PATCH 2/2] perf: Userspace software event and ioctl Message-ID: <20140924074942.GB3797@gmail.com> References: <1411050873-9310-1-git-send-email-pawel.moll@arm.com> <1411050873-9310-3-git-send-email-pawel.moll@arm.com> <1411491764.3922.46.camel@hornet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1411491764.3922.46.camel@hornet> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Pawel Moll wrote: > On Thu, 2014-09-18 at 15:34 +0100, Pawel Moll wrote: > > This patch adds a PERF_COUNT_SW_USERSPACE_EVENT type, > > which can be generated by user with PERF_EVENT_IOC_ENTRY > > ioctl command, which injects an event of said type into > > the perf buffer. > > It occurred to me last night that currently perf doesn't handle "write" > syscall at all, while this seems like the most natural way of > "injecting" userspace events into perf buffer. > > An ioctl would still be needed to set a type of the following events, > something like: > > ioctl(SET_TYPE, 0x42); > write(perf_fd, binaryblob, size); > ioctl(SET_TYPE, 0); > dprintf(perf_fd, "String"); > > which is fine for use cases when the type doesn't change often, > but would double the amount of syscalls when every single event > is of a different type. Perhaps there still should be a > "generating ioctl" taking both type and data/size in one go? Absolutely, there should be a single syscall. I'd even argue it should be a new prctl(): that way we could both generate user events for specific perf fds, but also into any currently active context (that allows just generation/injection of user events). In the latter case we might have no fd to work off from. And that is actually the really exciting usecase of your patches: we could generate user events via simple commands, and any external profiler/trace would be able to see them. Thanks, Ingo