On Mon, Nov 09, 2020 at 10:52:35AM +0100, Peter Zijlstra wrote: > On Fri, Nov 06, 2020 at 01:29:33PM -0800, kan.li...@linux.intel.com wrote: > > From: Kan Liang <kan.li...@linux.intel.com> > > > > Sometimes the PMU internal buffers have to be flushed for per-CPU events > > during a context switch, e.g., large PEBS. Otherwise, the perf tool may > > report samples in locations that do not belong to the process where the > > samples are processed in, because PEBS does not tag samples with PID/TID. > > > > The current code only flush the buffers for a per-task event. It doesn't > > check a per-CPU event. > > > > Add a new event state flag, PERF_ATTACH_SCHED_CB, to indicate that the > > PMU internal buffers have to be flushed for this event during a context > > switch. > > > > Add sched_cb_entry and perf_sched_cb_usages back to track the PMU/cpuctx > > which is required to be flushed. > > > > Only need to invoke the sched_task() for per-CPU events in this patch. > > The per-task events have been handled in perf_event_context_sched_in/out > > already. > > > > Fixes: 9c964efa4330 ("perf/x86/intel: Drain the PEBS buffer during context > > switches") > > Are you sure? In part this patch looks like a revert of: > > 44fae179ce73a26733d9e2d346da4e1a1cb94647 > 556cccad389717d6eb4f5a24b45ff41cad3aaabf
*groan*... I think I might've made a mistake with those two patches. I assumed the whole cpuctx->task_ctx thing was relevant, it is not. As per perf_sched_cb_{inc,dec}(struct pmu *), the thing we care about is that the *PMU* gets a context switch callback, we don't give a crap about the actual task context. Except that LBR code does, but I'm thinking that started the whole confusion -- and I'm still not sure it's actually correct either. Now,.. how did we end up with the above two patches anyway... /me frobs around in the inbox... Ah! that daft user RDPMC thing. I wanted to avoid yet another pmu::method(). Hmm.. and the reason I proposed that change is because we'd end up with the sched_cb for every context switch now, not just large-pebs and or lbr crud. And this form avoids the double perf_pmu_disable() and all that. Maybe we can frob x86_pmu_enable()...