linux-kernel - Re: [PATCH v1 7/7] perf cs-etm: Detect pid in VMID for kernel running at EL2

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Message-ID: <19205bb1-369a-9274-d752-d94f33a909f8@arm.com>
Date:   Mon, 11 Jan 2021 10:07:03 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Leo Yan <leo.yan@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Daniel Kiss <Daniel.Kiss@....com>,
        Denis Nikitin <denik@...omium.org>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Al Grant <al.grant@....com>
Subject: Re: [PATCH v1 7/7] perf cs-etm: Detect pid in VMID for kernel running
 at EL2

Hi Leo

On 1/9/21 7:44 AM, Leo Yan wrote:
> From: Suzuki K Poulose <suzuki.poulose@....com>
> 
> The pid of the task could be traced as VMID when the kernel is
> running at EL2. Teach the decoder to look for vmid when the
> context_id is invalid but we have a valid VMID.

Thank you again for cleaning up this ! Please see one comment
below.

> 
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Al Grant <al.grant@....com>
> Co-developed-by: Leo Yan <leo.yan@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>   .../perf/util/cs-etm-decoder/cs-etm-decoder.c | 32 ++++++++++++++++---
>   1 file changed, 28 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> index cd007cc9c283..9e81169dfa76 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> @@ -6,6 +6,7 @@
>    * Author: Mathieu Poirier <mathieu.poirier@...aro.org>
>    */
>   
> +#include <linux/coresight-pmu.h>
>   #include <linux/err.h>
>   #include <linux/list.h>
>   #include <linux/zalloc.h>
> @@ -500,13 +501,36 @@ cs_etm_decoder__set_tid(struct cs_etm_queue *etmq,
>   			const ocsd_generic_trace_elem *elem,
>   			const uint8_t trace_chan_id)
>   {
> -	pid_t tid;
> +	pid_t tid = -1;
> +	u64 pid_fmt;
> +	int ret;
>   
> -	/* Ignore PE_CONTEXT packets that don't have a valid contextID */
> -	if (!elem->context.ctxt_id_valid)
> +	ret = cs_etm__get_pid_fmt(trace_chan_id, &pid_fmt);
> +	if (ret)
> +		return OCSD_RESP_FATAL_SYS_ERR;

The patch looks fine to me. I am wondering if this can be cached somewhere in
the etmq to avoid doing the search everytime we hit a CID ? Surely for a session,
this woudn't change and thus for the decoder life time.

Cheers
Suzuki