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

[Arnaldo Carvalho de Melo]

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.

- Arnaldo
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