From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pawel Moll Subject: Re: [PATCH 2/2] perf: Userspace software event and ioctl Date: Thu, 25 Sep 2014 18:20:49 +0100 Message-ID: <1411665649.4768.84.camel@hornet> 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> <20140924074942.GB3797@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20140924074942.GB3797-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ingo Molnar Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Richard Cochran , Steven Rostedt , Peter Zijlstra , Paul Mackerras , John Stultz , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-api@vger.kernel.org On Wed, 2014-09-24 at 08:49 +0100, Ingo Molnar wrote: > * Pawel Moll wrote: >=20 > > 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. > >=20 > > It occurred to me last night that currently perf doesn't handle "wr= ite" > > syscall at all, while this seems like the most natural way of > > "injecting" userspace events into perf buffer. > >=20 > > An ioctl would still be needed to set a type of the following event= s, > > something like: > >=20 > > ioctl(SET_TYPE, 0x42); > > write(perf_fd, binaryblob, size); > > ioctl(SET_TYPE, 0); > > dprintf(perf_fd, "String"); > >=20 > > which is fine for use cases when the type doesn't change often,=20 > > but would double the amount of syscalls when every single event=20 > > is of a different type. Perhaps there still should be a=20 > > "generating ioctl" taking both type and data/size in one go? >=20 > Absolutely, there should be a single syscall. Yeah, it's my gut feeling as well. I just wonder if we still want to keep write() handler for operations on perf fds? This seems natural - takes data buffer and its size. The only issue is the type. > I'd even argue it should be a new prctl(): that way we could both=20 > generate user events for specific perf fds, but also into any=20 > currently active context (that allows just generation/injection=20 > of user events). In the latter case we might have no fd to work=20 > off from. When Arnaldo suggested that the "user events" could be used by perf trace, it was exactly my first thought. I just didn't have answer how t= o present it to the user (an extra syscall didn't seem like a good idea), but prctl seems interesting, something like this? prctl(PR_TRACE_UEVENT, type, size, data, 0); How would we select tasks that can write to a given buffer? Maybe an ioctl() on a perf fd? Something like this? ioctl(perf_fd, PERF_EVENT_IOC_ENABLE_UEVENT, pid); ioctl(perf_fd, PERF_EVENT_IOC_DISABLE_UEVENT, pid); It could set/clear a flag in pid's task_struct (but probably not in the "normal" flags, as they are only supposed to be set by owner and in ptrace/fork case) and a pointer to the task in perf_event(_context). Or maybe some variation on ptrace would be more in place? This would also solve issue of permission checking (if the profiling tool can ptrace the process, it can also enable/disable its uevent generation capability). Pawe=C5=82 Or maybe it should go through ptrace?