Re: [PATCH v5 1/4]: perf/core: use rb trees for pinned/flexible groups

From: Alexey Budankov
Date: Tue Jul 18 2017 - 09:39:47 EST


Hi,

On 18.07.2017 15:29, Alexander Shishkin wrote:
> Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> writes:
>
>> +/*
>> + * Helper function to test if event groups are empty;
>> + */
>> +static int
>> +perf_event_groups_empty(struct perf_event_groups *groups)
>> +{
>> + return list_empty(&groups->list);
>> +}
>
> This doesn't seem useful, it's only used once. Also, it's not clear how
> access to groups->list is serialized here, but it is in the caller.

Acepted. That API is removed in the final patch where list is replaced by rbtree.

>
> I'm assuming you will use this helper after the linked lists are done
> away with, but I'll have to go fishing for that patch to make sure.
>
>> +static void
>> +perf_event_groups_insert(struct perf_event_groups *groups,
>> + struct perf_event *event)
>> +{
>> + struct rb_node **node;
>> + struct rb_node *parent;
>> + struct perf_event *node_event;
>> +
>> + WARN_ON_ONCE(!groups || !event);
>
> I'm pretty sure neither of these is plausible.

Used that for debugging. Does it affect performance somehow?

>
>> + WARN_ON_ONCE(!list_empty(&event->group_list_entry));
>
> So ctx::lock is held here, right? That could be a useful assert and/or
> comment at least for review purposes. Now I see that it's called from
> list_add_event().

Agree.

>
> Regards,
> --
> Alex
>

Thanks,
Alexey