Re: [PATCH] perf record: Allow poll timeout to be specified

[Jiri Olsa <jolsa@redhat.com>]

On Tue, Mar 24, 2015 at 12:09:48PM -0400, David Ahern wrote:
> Record currently wakes up based on watermarks to read events from the mmaps and
> write them out to the file. The result is a file that can have large blocks of
> events per mmap before a finished round event is added to the stream.  This in
> turn affects the quantity of events that have to be passed through the ordered
> events queue before results can be displayed to the user. For commands like
> perf-script this can lead to long unnecessarily long delays before a user gets
> output. Large systems (e.g, 1024 cpus) further compound this effect. I have seen
> instances where I have to wait 45 minutes for perf-script to process a 5GB file
> before any events are shown.

so you have pipe to perf script, right?

> 
> This patch adds an option to perf-record to allow a user to specify the
> poll timeout in msec. For example using 100 msec timeouts similar to perf-top
> means the mmaps are traversed much more frequently leading to a smoother
> analysis side.

there's also the '--no-buffering' option that sets:

                attr->watermark = 0;
                attr->wakeup_events = 1;

but that's just the other edge, which is not what you'd want

I think it's good to have user side configurable as well

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka