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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