Re: tracing child threads with address filtering using intel_pt in perf

[Mansour Alharthi]

Thank you Alex for the prompt response and fix!

it works perfectly now..

Mansour..


On 10/08/2018 10:25 AM, Alexander Shishkin wrote:
> Alexander Shishkin  writes:
>
>> "Alharthi, Mansour A"  writes:
>>
>>> Hello all,
>> Hi,
>>
>>> Assume this test code:
>>>
>>> thread_start(){
>>> ...
>>> test();
>>> ...
>>> }
>>>
>>> test(){
>>> printf("test");
>>> }
>>>
>>> main(){
>>> ...
>>> pthread_create(.., thread_start,);
>>> }
>> Can you include the complete test case code?
>>
>>> Tracing the above program with the following command:
>>> perf record -v -m 512,1 -e intel_pt//u -T --switch-events --filter
>>> 'filter * @ ./test' -- ./test
>> Can you run it with -vvv and also include its output?
> Scratch that. Instead, can you try the below patch and see if it works
> for you?
>
> Thanks,
> --
> Alex
>
>  From 029a726b63ed6ebef527393704c83dab9c76fb9a Mon Sep 17 00:00:00 2001
> From: Alexander Shishkin 
> Date: Mon, 8 Oct 2018 17:16:30 +0300
> Subject: [PATCH] perf: Copy parent's address filter offsets on clone
>
> When a child event is allocated in the inherit_event() path, the VMA
> based filter offsets are not copied from the parent, even though the
> address space mapping of the new task remains the same, which leads
> to no trace for the new task until exec.
>
> Signed-off-by: Alexander Shishkin 
> ---
>   kernel/events/core.c | 15 +++
>   1 file changed, 15 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index c80549bf82c6..8cecbd61cd90 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1254,6 +1254,7 @@ static void put_ctx(struct perf_event_context *ctx)
>*perf_event_context::lock
>*  perf_event::mmap_mutex
>*  mmap_sem
> + * perf_addr_filters_head::lock
>*
>*cpu_hotplug_lock
>*  pmus_lock
> @@ -10058,6 +10059,20 @@ perf_event_alloc(struct perf_event_attr *attr, int 
> cpu,
>   goto err_per_task;
>   }
>   
> + /*
> +  * Clone the parent's vma offsets: they are valid until exec()
> +  * even if the mm is not shared with the parent.
> +  */
> + if (event->parent) {
> + struct perf_addr_filters_head *ifh = 
> perf_event_addr_filters(event);
> +
> + raw_spin_lock_irq(&ifh->lock);
> + memcpy(event->addr_filters_offs,
> +event->parent->addr_filters_offs,
> +pmu->nr_addr_filters * sizeof(unsigned long));
> + raw_spin_unlock_irq(&ifh->lock);
> + }
> +
>   /* force hw sync on the address filters */
>   event->addr_filters_gen = 1;
>   }

tracing child threads with address filtering using intel_pt pmu

[Mansour Alharthi]

Hello all,

I am having trouble tracing child threads when using address filtering 
with intel_pt ..

Assume this test code:

thread_start(){
...
test();
...
}

test(){
printf("test");
}

main(){
...
pthread_create(.., thread_start,);
}


Tracing the above program with the following command:
perf record -v -m 512,1 -e intel_pt//u -T --switch-events --filter 
'filter * @ ./test' -- ./test

Returns zero trace for code executed by child thread, i.e. 
thread_start() and test() functions..
While tracing without the filter does include the threads trace:
perf record -v -m 512,1 -e intel_pt//u -T --switch-events -- ./test

Is this intended? or is it a bug?

Thanks!
Mansour.

tracing child threads with address filtering using intel_pt

[Mansour Alharthi]

Hello all,

I am having trouble tracing child threads when using address filtering
with intel_pt ..

Assume this test code:

thread_start(){
...
test();
...
}

test(){
printf("test");
}

main(){
...
pthread_create(.., thread_start,);
}


Tracing the above program with the following command:
perf record -v -m 512,1 -e intel_pt//u -T --switch-events --filter
'filter * @ ./test' -- ./test

Returns zero trace for code executed by child thread, i.e.
thread_start() and test() functions..
While tracing without the filter does include the threads trace:
perf record -v -m 512,1 -e intel_pt//u -T --switch-events -- ./test

Is this intended? or is it a bug?

Thanks!
Mansour.