[ovs-dev] [PATCH 3/3] poll-loop: Log backtraces when CPU usage is high.

Ben Pfaff blp at nicira.com
Wed Oct 24 23:58:31 UTC 2012

On Wed, Oct 24, 2012 at 01:49:09PM -0700, Ethan Jackson wrote:
> Often when debugging Open vSwitch, one will see in the logs that
> CPU usage has been high for some period of time, but it's totally
> unclear why.  In an attempt to remedy the situation, this patch
> logs backtraces taken at regular intervals as a poor man's
> profiling alternative.
> Signed-off-by: Ethan Jackson <ethan at nicira.com>

I only have a minor cosmetic suggestion.  Here:

>      if (cpu_usage >= 0) {
>          ds_put_format(&s, " (%d%% CPU usage)", cpu_usage);
> +
> +        if (!vlog_should_drop(THIS_MODULE, level, &trace_rl)) {
> +            ds_put_cstr(&s, "\nBacktraces:\n");
> +            format_backtraces(&s, 2);
> +        }

it might make sense to drop "Backtraces:\n" (you probably want to keep
the newline) because otherwise if there aren't any repeated backtraces
or if we're on a system without backtrace() then you'll get a
funny-looking two-line log message without any additional detail.

Otherwise I think (hope, anyway) that this will be very useful.

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