linux-kernel - Re: [PATCH v5 4/4]: perf/core: complete replace of lists by rb trees for pinned and flexible groups at perf_event

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Message-ID: <dcf170c8-5096-4c4c-24a2-58e37c40d2d7@linux.intel.com>
Date:   Tue, 18 Jul 2017 16:38:39 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>, Kan Liang <kan.liang@...el.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@...el.com>,
        Valery Cherepennikov <valery.cherepennikov@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 4/4]: perf/core: complete replace of lists by rb trees
 for pinned and flexible groups at perf_event_context

Hi,

On 18.07.2017 15:40, Alexander Shishkin wrote:
> Alexey Budankov <alexey.budankov@...ux.intel.com> writes:
> 
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index 7b2cddf..8e1967f 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -603,13 +603,6 @@ struct perf_event {
>>  	 */
>>  	struct list_head		group_list;
>>  	/*
>> -	 * Entry into the group_list list above;
>> -	 * the entry may be attached to the self group_list list above
>> -	 * in case the event is directly attached to the tree;
>> -	 */
>> -	struct list_head		group_list_entry;
>> -
>> -	/*
>>  	 * We need storage to track the entries in perf_pmu_migrate_context; we
>>  	 * cannot use the event_entry because of RCU and we want to keep the
>>  	 * group in tact which avoids us using the other two entries.
> 
> You probably also want to explain this change, for example change the
> @group_list description, saying that something else links into it now.
> 

The whole patch as a single commit, attached to patch v5 4/4, may provide
the complete view of suggested changes.

>> @@ -749,15 +742,6 @@ struct perf_event {
>>  #endif /* CONFIG_PERF_EVENTS */
>>  };
>>  
>> -/*
>> - * event groups keep group leader events arranged as an rb tree with
>> - * event->cpu key and as a list for the whole tree iterations;
>> - */
>> -struct perf_event_groups {
>> -	struct list_head list;
>> -	struct rb_root	 tree;
>> -};
> 
> Was the @list component ever used? From this patch it looks like it
> wasn't and in reality you replaced the lists with trees is 1/4, but left
> the lists to hang around for a while.

list component was used starting from patch v5 1/4 till 3/4, and 4/4 
completely switched the list to rbtree. That was initial advice made
by Peter. He also suggested organizing patches in such a way so I 
implemented it.

> 
> I think a more generic comment here is that it's difficult to review
> patches that don't make sense in separation from one another. It does
> make sense to make a transition across several patches, but each patch
> kind of needs to make sense on its own. For example, 1/2 adds trees
> while keeping the lists intact, 2/2 removes the lists.
> 

Agree. That was my intention - try to split the whole work into logically
connected steps and simplify review process and make reviewers work easier.

> Regards,
> --
> Alex
> 

Thanks,
Alexey