Messages in this thread | | | Subject | Re: [PATCH] perf, core: Fix initial task_ctx/event installation | From | Peter Zijlstra <> | Date | Mon, 06 Jun 2011 19:40:26 +0200 |
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It helps if you actually use the right email address for me ;-)
On Mon, 2011-06-06 at 16:38 +0200, Jiri Olsa wrote: > hi, > > I think I found a bug in the __perf_install_in_context. The attached > patch fixies the problem for me, but I'm not sure it did not break > anything else.. ;) > > thanks, > jirka > > --- > The __perf_install_in_context function does not install context > events in case there's no active task context. > > This might cause incorrect counts if application opens counter > in its own task context. > > Following scenario leads to wrong counts: > (this is the case for "perf test - test__open_syscall_event > which counts sys_enter_open calls) > > 1 - application is scheduled in > 2 - application enters perf_event_open syscall with its own pid > 3 - event/context is created > 4 - __perf_install_in_context is called > 5 - cpuctx->task_ctx is NULL > 6 - perf_event_sched_in gets called with ctx == NULL, new event is not scheduled in > 7 - application leaves the perf_event_open syscall > 8 - application running code leading to increment the event counter > !!! this is where we lost the counts, since the event is not scheduled in !!! > 9 - application is scheduled out > 11 - application is scheduled in > 12 - event is properly sceduled in > 13 - event counter is now incremented > > If the task is scheduled out and back in after the context is installed, > but before it exits the perf_event_open syscall, the task_ctx gets > properly set and event is properly scheduled in. In this case > the perf test returns proper counts. > > Attached patch changed this behaviour to install new task_ctx > even if the current task_ctx is NULL. > > Tested by succesfully running perf test command.
Right, so I have those bits as per https://lkml.org/lkml/2011/4/10/17, they got lost in the commit due to a quilt refresh boo-boo.
With these bits it works on my dual core, but I still get lockups on my 24-cpu wsm machine.
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