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In-Reply-To: <20190822090555.GJ2349@hirez.programming.kicks-ass.net>
Date:   Thu, 22 Aug 2019 14:08:10 -0700
Cc:     "Yonghong Song" <yhs@fb.com>, "Daniel Xu" <dxu@dxuuu.xyz>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        "Andrii Nakryiko" <andriin@fb.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "acme@kernel.org" <acme@kernel.org>,
        "Alexei Starovoitov" <ast@fb.com>,
        "alexander.shishkin@linux.intel.com" 
        <alexander.shishkin@linux.intel.com>,
        "jolsa@redhat.com" <jolsa@redhat.com>,
        "namhyung@kernel.org" <namhyung@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Kernel Team" <Kernel-team@fb.com>,
        "Arnaldo Carvalho de Melo" <acme@redhat.com>
Subject: Re: [PATCH v3 bpf-next 1/4] tracing/probe: Add
 PERF_EVENT_IOC_QUERY_PROBE ioctl
From:   "Daniel Xu" <dxu@dxuuu.xyz>
To:     "Peter Zijlstra" <peterz@infradead.org>,
        "Song Liu" <songliubraving@fb.com>
Message-Id: <BWGGRTQXX7EP.15IPIDK3KLQ6O@dlxu-fedora-R90QNFJV>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu Aug 22, 2019 at 11:05 AM Peter Zijlstra wrote:
> On Thu, Aug 22, 2019 at 07:54:16AM +0000, Song Liu wrote:
> > Hi Peter,=20
> >=20
> > > On Aug 22, 2019, at 12:47 AM, Peter Zijlstra <peterz@infradead.org> w=
rote:
> > >=20
> > > On Wed, Aug 21, 2019 at 06:43:49PM +0000, Yonghong Song wrote:
> > >> On 8/21/19 11:31 AM, Peter Zijlstra wrote:
> > >=20
> > >>> So extending PERF_RECORD_LOST doesn't work. But PERF_FORMAT_LOST mi=
ght
> > >>> still work fine; but you get to implement it for all software event=
s.
> > >>=20
> > >> Could you give more specifics about PERF_FORMAT_LOST? Googling=20
> > >> "PERF_FORMAT_LOST" only yields two emails which we are discussing he=
re :-(
> > >=20
> > > Look at what the other PERF_FORMAT_ flags do? Basically it is adding =
a
> > > field to the read(2) output.
> >=20
> > Do we need to implement PERF_FORMAT_LOST for all software events? If us=
er
> > space asks for PERF_FORMAT_LOST for events that do not support it, can =
we
> > just fail sys_perf_event_open()?
>=20
> It really shouldn't be hard; and I'm failing to see why kprobes are
> special.

Thanks for the feedback, everyone. Really appreciate it.

I will look into extending read_format. I'll submit another patch series
after I get the code to work.

Daniel