[lkml]   [2018]   [Feb]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] perf: Add support for creating offline events

On 02/13/2018 08:08 AM, Jiri Olsa wrote:
> On Mon, Feb 12, 2018 at 02:22:30PM -0800, Raghavendra Rao Ananta wrote:
>> On 02/12/2018 01:21 PM, Jiri Olsa wrote:
>>> On Mon, Feb 12, 2018 at 10:04:42PM +0100, Jiri Olsa wrote:
>>>> On Mon, Feb 12, 2018 at 09:42:05AM -0800, Raghavendra Rao Ananta wrote:
>>>>> Hi Jiri,
>>>>> Thank you for the response.
>>>>> Does perf tool has its own check to see if the CPU was offline during the
>>>>> lifetime of an event? If so, it might ignore these type of events.
>>>> nope, we don't check on that
>>>>> Initially, I tested the same using perf tool and found similar results.
>>>>> Then I debugged further and found that the perf core was actually sending
>>>>> data to the userspace (copy_to_user()) and the corresponding count for the
>>>>> data. Hence, I tested this further by writing my own userspace application,
>>>>> and I was able to read the count through this,
>>>>> even when the CPU was made offline and back online.
>>>>> Do you think we also have to modify the perf tool accordingly?
>>>> hum, I wonder what's wrong.. will check
>>> I think the user space needs to enable the event once the
>>> cpu gets online.. which we dont do and your app does..?
>>> maybe we could add perf_event_attr::enable_on_online ;-)
>>> I'll check what we can do in user space, I guess we can
>>> monitor the cpu state and enable event accordingly
>>> jirka
>> Yes, probably that's the reason.
>> In order for an event to get scheduled-in, it expects the event to be at
>> least in PERF_EVENT_STATE_INACTIVE state. If you notice, in my patch,
>> when the cpu wakes up, we are initializing the state of the event
>> (perf_event__state_init()) and then trying to schedule-in. Since the event
>> was created with a disabled state, it seems that the same this is followed
>> and the state gets initialized to PERF_EVENT_STATE_OFF. Unfortunately,
>> events in this state could not be scheduled.
>> One way for things to get working is, instead of calling
>> perf_event__state_init() before the event is scheduled-in (when the cpu
>> wakes up), we can do something like:
>> perf_event_set_state(event, PERF_EVENT_STATE_INACTIVE);
> could you add check in ioctl call that set the inactive state
> on the dormant event.. that would start it once the cpu is
> online.. as requested

I am a little confused. When you say "check", do you mean a new ioctl

So the flow (from the user-space perspective) would go something like this?

1. // CPU offline

2. perf_event_open(); // event started as disabled --> added to dormant
list in the kernel

3. ioctl(SET_INACTIVE); // change the state of the event to inactive

4. // CPU woken up!

5. // schedule the (inactive) event by traversing the dormant list

Is this what you were trying to mention, or am I missing something?

Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

 \ /
  Last update: 2018-02-13 19:03    [W:0.142 / U:0.728 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site