Re: [RFC 2/2] perf: Marker software event and ioctl

[David Ahern]

On 9/12/14, 2:44 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Sep 12, 2014 at 10:37:39AM -0700, David Ahern escreveu:
> > On 9/12/14, 4:48 AM, Pawel Moll wrote:
> > > This patch adds a PERF_COUNT_SW_MARKER event type, which
> > > can be requested by user and a PERF_EVENT_IOC_MARKER
> > > ioctl command which will inject an event of said type into
> > > the perf buffer. The ioctl can take a zero-terminated
> > > string argument, similar to tracing_marker in ftrace,
> > > which will be kept in the "raw" field of the sample.
> > >
> > > The main use case for this is synchronisation of
> > > performance data generated in user space with the perf
> > > stream coming from the kernel. For example, the marker
> > > can be inserted by a JIT engine after it generated
> > > portion of the code, but before the code is executed
> > > for the first time, allowing the post-processor to
> > > pick the correct debugging information. Other example
> > > is a system profiling tool taking data from other
> > > sources than just perf, which generates a marker
> > > at the beginning at at the end of the session
> > > (also possibly periodically during the session) to
> > > synchronise kernel timestamps with clock values
> > > obtained in userspace (gtod or raw_monotonic).
> >
> > Seems really similar to what I proposed in the past:
> >
> > https://lkml.org/lkml/2011/2/27/159
> >
> > Which was rejected.
>
> I took a look at that thread, but just barely, emphasis on that.
>
> Injecting something from userspace, a la ftrace, seems to be something,
> as tglx mentioned, "buried" in that patchset.

Thomas object to an ioctl buried deep in a patch -- newbie mistake.

Peter objected to the ioctl https://lkml.org/lkml/2011/3/1/229

It was not userspace injecting random data into the stream but rather 
forcing the sample to be generated and added to the stream.

David

David


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