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SubjectRe: Latency issues with x86.git

* Kevin Winchester <kjwinchester@gmail.com> wrote:

> Hi Ingo,
>
> I have encountered (a handful of times in the past few months) some
> real interactivity problems on my system. Moving the mouse or typing
> a key on the keyboard takes around a second to show any response.
> Once I perform a reboot, the problem is gone again. I am currently
> running x86.git mm branch, but I switch between that branch, mainline
> git, and mm kernels, so I cannot guarantee on which trees I have or
> have not seen the problem.

please try sched-devel.git, which has both the latest scheduler fixes,
and also the new "ftrace" latency tracing framework that can be used to
trace various latency problems. You can pick up sched-devel.git via:

http://people.redhat.com/mingo/sched-devel.git/README

firstly, there's a chance that sched-devel.git solves the problem - in
that case please report it.

if it doesnt, then you can trace various latencies via these:

CONFIG_FTRACE=y
CONFIG_IRQSOFF_TRACER=y
CONFIG_SCHED_TRACER=y
CONFIG_CONTEXT_SWITCH_TRACER=y
CONFIG_DYNAMIC_FTRACE=y

just enable them, boot into the new kernel and mount debugfs:

mount -t debugfs nodev /debug

and then you can select one of the tracers (that have been enabled in
the .config) via /debug/tracing/* files. The usage of these files should
be self-explaining - if any of them wasnt then please let us know and
we'll make the "first quick glance experience" better :)

the one interesting to you would be the "wakeup" tracer. Enable it, and
if you echo 0 into /debug/tracing/tracing_max_latency it starts tracking
the worst-case delay experienced on your system and should start
reporting them to the syslog.

if you encounter any problems during these steps then please let us know
- this code is quite fresh so expect some rough edges.

Ingo


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