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SubjectRe: [RFC 2/2] perf: Sharing PMU counters across compatible events
On Fri, May 04, 2018 at 04:11:02PM -0700, Song Liu wrote:
> +static void add_event_to_dup_event_list(struct perf_event *event,
> + struct perf_cpu_context *cpuctx)
> +{
> + int i;
> +
> + for (i = 0; i < cpuctx->dup_event_count; ++i)
> + if (memcmp(&event->attr,
> + &cpuctx->dup_event_list[i].first->attr,
> + sizeof(event->attr)) == 0) {
> + event->dup_id = i;
> + return;
> + }
> + i = cpuctx->dup_event_count++;
> + cpuctx->dup_event_list[i].first = event;
> + cpuctx->dup_event_list[i].master = NULL;
> + INIT_LIST_HEAD(&cpuctx->dup_event_list[i].active_dup);
> + event->dup_id = i;
> + INIT_LIST_HEAD(&event->dup_sibling_entry);
> +}
> +
> +static int add_group_to_dup_event_list(struct perf_event *event, void *data)
> +{
> + struct sched_in_data *sid = data;
> + struct perf_event *sibling;
> +
> + add_event_to_dup_event_list(event, sid->cpuctx);
> + for_each_sibling_event(sibling, event)
> + add_event_to_dup_event_list(sibling, sid->cpuctx);
> +
> + return 0;
> +}
> +
> +static void rebuild_event_dup_list(struct perf_cpu_context *cpuctx)
> +{
> + int dup_count = cpuctx->ctx.nr_events;
> + struct perf_event_context *ctx = cpuctx->task_ctx;
> + struct sched_in_data sid = {
> + .ctx = ctx,
> + .cpuctx = cpuctx,
> + .can_add_hw = 1,
> + };
> +
> + if (ctx)
> + dup_count += ctx->nr_events;
> +
> + kfree(cpuctx->dup_event_list);
> + cpuctx->dup_event_count = 0;
> +
> + cpuctx->dup_event_list =
> + kzalloc(sizeof(struct perf_event_dup) * dup_count, GFP_ATOMIC);
> + if (!cpuctx->dup_event_list)
> + return;
> +
> + visit_groups_merge(&cpuctx->ctx.pinned_groups, smp_processor_id(),
> + add_group_to_dup_event_list, &sid);
> + visit_groups_merge(&cpuctx->ctx.flexible_groups, smp_processor_id(),
> + add_group_to_dup_event_list, &sid);
> + if (ctx) {
> + visit_groups_merge(&ctx->pinned_groups, smp_processor_id(),
> + add_group_to_dup_event_list, &sid);
> + visit_groups_merge(&ctx->flexible_groups, smp_processor_id(),
> + add_group_to_dup_event_list, &sid);
> + }
> +}

Oooh, wait a second, this isn't O(n), this looks like O(n^2).

We do that linear search for every single event... that's not good.

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