Messages in this thread | | | Subject | Re: [PATCH] perf: Add support for creating offline events | From | Raghavendra Rao Ananta <> | Date | Tue, 13 Feb 2018 10:03:04 -0800 |
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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 command?
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?
Raghavendra -- Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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