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

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Date:   Mon, 11 Jan 2021 21:10:08 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     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,
        Al Grant <al.grant@....com>
Subject: Re: [PATCH v1 7/7] perf cs-etm: Detect pid in VMID for kernel
 running at EL2

On Mon, Jan 11, 2021 at 10:07:03AM +0000, Suzuki Kuruppassery Poulose wrote:
> 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.

Welcome!

> > 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.

Good suggestion, will refine for this in next version.

Thanks,
Leo