Messages in this thread Patch in this message | | | Date | Thu, 17 Jun 2021 13:33:00 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 0/4] perf: Fix the ctx->pmu for a hybrid system |
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On Thu, Jun 17, 2021 at 12:23:06PM +0200, Peter Zijlstra wrote: > On Wed, Jun 16, 2021 at 11:55:30AM -0700, kan.liang@linux.intel.com wrote: > > > To fix the issue, the generic perf codes have to understand the > > supported CPU mask of a specific hybrid PMU. So it can update the > > ctx->pmu accordingly, when a task is scheduled on a CPU which has > > a different type of PMU from the previous CPU. The supported_cpus > > has to be moved to the struct pmu. > > Urghh.. I so hate this :-/ > > I *did* point you to: > > https://lore.kernel.org/lkml/20181010104559.GO5728@hirez.programming.kicks-ass.net/ > > when you started this whole hybrid crud, and I think that's still the > correct thing to do. > > Still, let me consider if there's a workable short-term cludge I hate > less.
How's this? We already have x86_pmu_update_cpu_context() setting the 'correct' pmu in the cpuctx, so we can simply fold that back into the task context.
For normal use this is a no-op.
Now I need to go audit all ctx->pmu usage :-(
--- diff --git a/kernel/events/core.c b/kernel/events/core.c index db4604c4c502..6a496c29ef00 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3822,9 +3822,16 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx, struct task_struct *task) { struct perf_cpu_context *cpuctx; - struct pmu *pmu = ctx->pmu; + struct pmu *pmu; cpuctx = __get_cpu_context(ctx); + + /* + * HACK; for HETEROGENOUS the task context might have switched to a + * different PMU, don't bother gating this. + */ + pmu = ctx->pmu = cpuctx->ctx.pmu; + if (cpuctx->task_ctx == ctx) { if (cpuctx->sched_cb_usage) __perf_pmu_sched_task(cpuctx, true);
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