Re: [PATCH v2]: perf/core: addressing 4x slowdown during per-process, profiling of STREAM benchmark on Intel Xeon Phi

[Alexey Budankov <alexey.budankov@linux.intel.com>]

On 29.05.2017 10:45, Peter Zijlstra wrote:
> On Sat, May 27, 2017 at 02:19:51PM +0300, Alexey Budankov wrote:
>> Solution:
>>
>> cpu indexed trees for perf_event_context::pinned_groups and
>> perf_event_context::flexible_groups lists are introduced. Every tree node
>> keeps a list of groups allocated for the same cpu. A tree references only
>> groups located at the appropriate group list. The tree provides capability
>> to iterate over groups allocated for a specific cpu only, what is exactly
>> required by multiplexing timer interrupt handler. The handler runs per-cpu
>> and enables/disables groups using group_sched_in()/group_sched_out() that
>> call event_filter_match() function filtering out groups allocated for cpus
>> different from the one executing the handler. Additionally for every
>> filtered out group group_sched_out() updates tstamps values to the current
>> interrupt time. This updating work is now done only once by
>> update_context_time() called by ctx_sched_out() before cpu groups
>> iteration. For this trick to work it is required that tstamps of filtered
>> out events would point to perf_event_context::tstamp_data object instead
>> of perf_event::tstamp_data ones, as it is initialized from an event
>> allocation. tstamps references are switched by
>> group_sched_in()/group_sched_out() every time a group is checked for its
>> suitability for currently running cpu. When a thread enters some cpu on
>> a context switch a long run through pinned and flexible groups is
>> performed by perf_event_sched_in(, mux=0) with new parameter mux set to 0
>> and filtered out groups tstamps are switched to
>> perf_event_context::tstamp_data object. Then a series of multiplexing
>> interrupts happens and the handler rotates the flexible groups calling
>> ctx_sched_out(,mux=1)/perf_event_sched_in(,mux=1) iterating over the cpu
>> tree lists only and avoiding long runs through the complete group lists.
>> This is where speedup comes from. Eventually when the thread leaves the cpu
>> ctx_sched_out(,mux=0) is called restoring tstamps pointers to the events'
>> perf_event::tstamp_data objects.
> 
> This is unreadable.. Please use whitespace.

Do you mean do NOT use whitespaces? Could you explain in more detail 
what you mean?

> 
> 
>> Added API:
>>
>> Objects:
>> 1. struct perf_event_tstamp:
>>     - enabled
>>     - running
>>     - stopped
>> 2. struct perf_event:
>>     - group_node
>>     - group_list
>>     - group_list_entry
>>     - tstamp
>>     - tstamp_data
>> 3. struct perf_event_context:
>>     - pinned_tree
>>     - flexible_tree
>>     - tstamp_data
>>
>> Functions:
>> 1. insert a group into a tree using event->cpu as a key:
>> 	int perf_cpu_tree_insert(struct rb_root *tree,
>> 		struct perf_event *event);
>> 2. delete a group from a tree, if the group is directly attached
>>     to a tree it also detaches all groups on the groups
>>     group_list list:
>> 	int perf_cpu_tree_delete(struct rb_root *tree,
>> 		struct perf_event *event);
>> 3. find group_list list by a cpu key:
>>          struct list_head * perf_cpu_tree_find(struct rb_root *tree,
>> 		int cpu);
>> 4. enable a pinned group on a cpu:
>>          void ctx_sched_in_flexible_group(struct perf_event_context *ctx,
>> 		struct perf_cpu_context *cpuctx,
>> 		struct perf_event *group, int *can_add_hw);
>> 5. enable a flexible group on a cpu; calls ctx_sched_in_flexible_group
>>     and updates group->state to ERROR in case of failure:
>> 	void ctx_sched_in_pinned_group(struct perf_event_context *ctx,
>> 		struct perf_cpu_context *cpuctx,
>> 		struct perf_event *group);
>> 6. enable per-cpu pinned tree's groups on a cpu:
>> 	void ctx_pinned_sched_in_groups(struct perf_event_context *ctx,
>> 		struct perf_cpu_context *cpuctx,
>> 		struct list_head *groups);
>> 7. enable per-cpu flexible tree's groups on a cpu:
>> 	void ctx_flexible_sched_in_groups(
>> 		struct perf_event_context *ctx,
>> 		struct perf_cpu_context *cpuctx,
>> 		struct list_head *groups);
>> 8. disable per-cpu tree's groups on a cpu:
>> 	void ctx_sched_out_groups(struct perf_event_context *ctx,
>> 		struct perf_cpu_context *cpuctx,
>> 		struct list_head *groups);
>> 9. get a group tree based on event->attr.pinned attribute value:
>> 	struct rb_root * ctx_cpu_tree(struct perf_event *event,
>> 		struct perf_event_context *ctx);
>>
>> Modified API:
>>
>> Objects:
>> 1. struct perf_event
>> 2. struct perf_event_context
>>
>> Functions:
>> 1. perf_event_alloc()
>> 2. add_event_to_ctx()
>> 3. perf_event_enable_on_exec()
>> 4. __perf_install_in_context()
>> 5. __perf_event_init_context()
>> 6. __perf_event_mark_enabled()
>> 7. __perf_event_enable()
>> 8. __perf_event_task_sched_out()
>> 9. ctx_group_list()
>> 10. list_add_event()
>> 11. list_del_event()
>> 12. perf_event_context_sched_in()
>> 13. cpu_ctx_sched_in()
>> 14. cpu_ctx_sched_out()
>> 15. ctx_sched_in()
>> 16. ctx_sched_out()
>> 17. ctx_resched()
>> 18. ctx_pinned_sched_in()
>> 19. ctx_flexible_sched_in()
>> 20. group_sched_in()
>> 21. event_sched_in()
>> 22. event_sched_out()
>> 23. rotate_ctx()
>> 24. perf_rotate_context()
>> 25. update_context_time()
>> 26. update_event_times()
>> 27. calc_timer_values()
>> 28. perf_cgroup_switch()
>> 29. perf_cgroup_mark_enabled()
> 
> Yeah, this doesn't go into a changelog. Have you _ever_ seen a changelog
> with such crud in?
> 

I have not. Could you please advise how to format this information to be 
suitable for changelog, if it's required at all?

Thanks,
Alexey