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SubjectRe: [PATCH V2 04/23] perf/x86/intel: Support adaptive PEBSv4
On Thu, Mar 21, 2019 at 01:56:44PM -0700, kan.liang@linux.intel.com wrote:
> @@ -933,6 +1001,34 @@ pebs_update_state(bool needed_cb, struct cpu_hw_events *cpuc, struct pmu *pmu)
> update = true;
> }
>
> + /*
> + * The PEBS record doesn't shrink on the del. Because to get
> + * an accurate config needs to go through all the existing pebs events.
> + * It's not necessary.
> + * There is no harmful for a bigger PEBS record, except little
> + * performance impacts.
> + * Also, for most cases, the same pebs config is applied for all
> + * pebs events.
> + */
> + if (x86_pmu.intel_cap.pebs_baseline && add) {
> + u64 pebs_data_cfg;
> +
> + /* Clear pebs_data_cfg and pebs_record_size for first PEBS. */
> + if (cpuc->n_pebs == 1) {
> + cpuc->pebs_data_cfg = 0;
> + cpuc->pebs_record_size = sizeof(struct pebs_basic);
> + }

Argh, no. This is daft. The previous site was fine, it was just the
pebs_record_size assignment I'm confused about.

Note how by setting ->pebs_data_cfs to 0, you force the below branch to
true and call adaptive_pebs_record_size_update() ? So _why_ do you have
to set pebs_record_size()?

> +
> + pebs_data_cfg = pebs_update_adaptive_cfg(event);
> +
> + /* Update pebs_record_size if new event requires more data. */
> + if (pebs_data_cfg & ~cpuc->pebs_data_cfg) {
> + cpuc->pebs_data_cfg |= pebs_data_cfg;
> + adaptive_pebs_record_size_update();
> + update = true;
> + }
> + }
> +
> if (update)
> pebs_update_threshold(cpuc);
> }

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