Re: [PATCH v2 01/18] perf cs-etm: Queue context packets for frontend

[Leo Yan <leo.yan@arm.com>]

On Tue, Jun 02, 2026 at 03:26:43PM +0100, James Clark wrote:

[...]

> @@ -614,10 +621,12 @@ static int cs_etm__init_traceid_queue(struct cs_etm_queue *etmq,
>  
>  	queue = &etmq->etm->queues.queue_array[etmq->queue_nr];
>  	tidq->trace_chan_id = trace_chan_id;
> -	tidq->el = tidq->prev_packet_el = ocsd_EL_unknown;
> -	tidq->thread = machine__findnew_thread(&etm->session->machines.host, -1,
> +	tidq->decode_el = ocsd_EL_unknown;
> +	tidq->frontend_thread = machine__findnew_thread(&etm->session->machines.host, -1,
> +					       queue->tid);
> +	tidq->decode_thread = machine__findnew_thread(&etm->session->machines.host, -1,
>  					       queue->tid);
> -	tidq->prev_packet_thread = machine__idle_thread(&etm->session->machines.host);
> +

Redundant new line.

>  	tidq->packet = zalloc(sizeof(struct cs_etm_packet));
>  	if (!tidq->packet)
> @@ -751,20 +760,16 @@ static void cs_etm__packet_swap(struct cs_etm_auxtrace *etm,
>  		 * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for
>  		 * the next incoming packet.
>  		 *
> -		 * Threads and exception levels are also tracked for both the
> -		 * previous and current packets. This is because the previous
> -		 * packet is used for the 'from' IP for branch samples, so the
> -		 * thread at that time must also be assigned to that sample.
> -		 * Across discontinuity packets the thread can change, so by
> -		 * tracking the thread for the previous packet the branch sample
> -		 * will have the correct info.
> +		 * Track Exception levels for both the previous and current
> +		 * packets. This is because the previous packet's address is
> +		 * used for the 'from' IP for branch samples, so the previous EL
> +		 * must also be used so that sample shows it originates from the
> +		 * correct EL. Branches can't branch to a different thread, so
> +		 * no need to track the previous thread.
>  		 */
>  		tmp = tidq->packet;
>  		tidq->packet = tidq->prev_packet;
>  		tidq->prev_packet = tmp;
> -		tidq->prev_packet_el = tidq->el;
> -		thread__put(tidq->prev_packet_thread);
> -		tidq->prev_packet_thread = thread__get(tidq->thread);

As here no any code for EL swap, the comment above is a bit disconnected
with the code. Can we just remove the comment to avoid confusion?

Otherwise, looks good. Thanks for maturing the patch.

Leo