Messages in this thread | | | Date | Tue, 3 May 2011 23:41:45 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC PATCH] tracing: Don't call wakeup() when committing the event |
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On Tue, May 03, 2011 at 02:03:36PM -0700, Vaibhav Nagarnaik wrote: > In using syscall tracing by concurrent processes, the wakeup() that is > called in the event commit function causes contention on the spin lock > of the waitqueue. I enabled sys_enter_getuid and sys_exit_getuid > tracepoints, and by running getuid_microbench from autotest in parallel > I found that the contention causes exponential latency increase in the > tracing path. > > The autotest binary getuid_microbench calls getuid() in a tight loop for > the given number of iterations and measures the average time required to > complete a single invocation of syscall. > > The patch here points to the problem and provides a naive solution to > start the discussion. It is not intended to be a definitive solution.
Right, so another solution could be to have per cpu waitqueues for the per_cpu trace_pipe/trace_pipe_raw files, and one big for the main trace_pipe file.
That involves two wake_up() calls but then it scales and you keep the awakening.
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