Messages in this thread | | | Date | Thu, 4 Jul 2013 14:44:08 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 4/7] perf, x86: Save/resotre LBR stack during context switch |
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On Mon, Jul 01, 2013 at 03:23:04PM +0800, Yan, Zheng wrote: > From: "Yan, Zheng" <zheng.z.yan@intel.com> > > When the LBR call stack is enabled, it is necessary to save/restore > the LBR stack on context switch. The solution is saving/restoring > the LBR stack to/from task's perf event context. > > If there are cpu-wide events that use LBR, do not save/restore the > LBR stack on context switches, flush it instead.
Again inadequate changelog; it fails to explain wtf this is:
> + if (event->ctx->task && > + branch_user_callstack(event->hw.branch_reg.reg)) { > + struct x86_perf_event_context *task_ctx = (void *)event->ctx; > + /* > + * Reset the LBR stack if the call stack is not > + * continuous enabled > + */ > + if (task_ctx->lbr_callstack_users == 0 && > + task_ctx->lbr_stack_gen + 1 < event->ctx->sched_gen) > + intel_pmu_lbr_reset(); > + > + task_ctx->lbr_callstack_users++; > + task_ctx->lbr_stack_gen = event->ctx->sched_gen; > + } > }
And what this parent_ctx nonsense is about:
> +void intel_pmu_lbr_init_context(struct perf_event_context *child_ctx, > + struct perf_event_context *parent_ctx) > +{ > + struct x86_perf_event_context *task_ctx, *parent_task_ctx; > + > + if (!x86_pmu.lbr_nr) > + return; > + > + task_ctx = (struct x86_perf_event_context *)child_ctx; > + parent_task_ctx = (struct x86_perf_event_context *)parent_ctx; > + > + if (parent_task_ctx->lbr_callstack_users) > + __intel_pmu_lbr_save(task_ctx); > + else > + task_ctx->lbr_stack_saved = false; > +}
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