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

[Mansour Alharthi <malharthi9@gatech.edu>]

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 <alexander.shishkin@linux.intel.com> writes:
>
>> "Alharthi, Mansour A" <mansourah@gatech.edu> 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 512,10000 -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 <alexander.shishkin@linux.intel.com>
> 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 <alexander.shishkin@linux.intel.com>
> ---
>   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;
>   	}