linux-kernel - Re: [tip:perf/core] perf/core: Add a flag for partial AUX records

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Message-ID: <alpine.DEB.2.20.1703161021460.695@macbook-air>
Date:   Thu, 16 Mar 2017 10:24:53 -0400 (EDT)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     hpa@...or.com, torvalds@...ux-foundation.org, eranian@...gle.com,
        peterz@...radead.org, alexander.shishkin@...ux.intel.com,
        mingo@...nel.org, acme@...radead.org, tglx@...utronix.de,
        jolsa@...hat.com, linux-kernel@...r.kernel.org,
        vincent.weaver@...ne.edu, mathieu.poirier@...aro.org,
        acme@...hat.com
cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/core: Add a flag for partial AUX records

On Thu, 16 Mar 2017, tip-bot for Alexander Shishkin wrote:

> Commit-ID:  ae0c2d995d648d5165545d5e05e2869642009b38

> perf/core: Add a flag for partial AUX records
> 
> The Intel PT driver needs to be able to communicate partial AUX transactions,
> that is, transactions with gaps in data for reasons other than no room
> left in the buffer (i.e. truncated transactions). Therefore, this condition
> does not imply a wakeup for the consumer.
> 
> To this end, add a new "partial" AUX flag.

...

> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index bec0aad..d09a9cd 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -915,6 +915,7 @@ enum perf_callchain_context {
>   */
>  #define PERF_AUX_FLAG_TRUNCATED		0x01	/* record was truncated to fit */
>  #define PERF_AUX_FLAG_OVERWRITE		0x02	/* snapshot from overwrite mode */
> +#define PERF_AUX_FLAG_PARTIAL		0x04	/* record contains gaps */


was this included in the wrong patch?  It adds the flag but nothing uses 
it?  Though it appears a later patch makes use of it.  

This makes it confusing when trying to update the perf_event_open.2 
manpage, as the git commit that adds the new ABI to perf_event.h doesn't 
seem to have anything to do with any behavior affected by it.

>  #define PERF_FLAG_FD_NO_GROUP		(1UL << 0)
>  #define PERF_FLAG_FD_OUTPUT		(1UL << 1)
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 9654e55..2831480 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -424,8 +424,8 @@ err:
>   */
>  void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
>  {
> +	bool wakeup = !!(handle->aux_flags & PERF_AUX_FLAG_TRUNCATED);
>  	struct ring_buffer *rb = handle->rb;
> -	bool wakeup = !!handle->aux_flags;
>  	unsigned long aux_head;
>