linux-kernel - Re: [PATCH v2 5/7] perf cs-etm: Add helper cs_etm__get_pid

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Date:   Thu, 4 Feb 2021 11:47:43 +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>,
        Jonathan Corbet <corbet@....net>,
        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-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/7] perf cs-etm: Add helper cs_etm__get_pid_fmt()

On Tue, Feb 02, 2021 at 11:19:22PM +0000, Suzuki Kuruppassery Poulose wrote:
> On 2/2/21 4:38 PM, Leo Yan wrote:
> > This patch adds helper function cs_etm__get_pid_fmt(), by passing
> > parameter "traceID", it returns the PID format.
> > 
> > Signed-off-by: Leo Yan <leo.yan@...aro.org>
> > ---
> >   tools/perf/util/cs-etm.c | 43 ++++++++++++++++++++++++++++++++++++++++
> >   tools/perf/util/cs-etm.h |  1 +
> >   2 files changed, 44 insertions(+)
> > 
> > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > index a2a369e2fbb6..8194ddbd01e5 100644
> > --- a/tools/perf/util/cs-etm.c
> > +++ b/tools/perf/util/cs-etm.c
> > @@ -7,6 +7,7 @@
> >    */
> >   #include <linux/bitops.h>
> > +#include <linux/coresight-pmu.h>
> >   #include <linux/err.h>
> >   #include <linux/kernel.h>
> >   #include <linux/log2.h>
> > @@ -156,6 +157,48 @@ int cs_etm__get_cpu(u8 trace_chan_id, int *cpu)
> >   	return 0;
> >   }
> > +/*
> > + * The returned PID format is presented by two bits:
> > + *
> > + *   Bit ETM_OPT_CTXTID: CONTEXTIDR or CONTEXTIDR_EL1 is traced;
> > + *   Bit ETM_OPT_CTXTID2: CONTEXTIDR_EL2 is traced.
> > + *
> > + * It's possible that these two bits are set together, this means the tracing
> > + * contains PIDs for both CONTEXTIDR_EL1 and CONTEXTIDR_EL2.
> 
> This is a bit confusing. If both the bits are set, the session
> was run on an EL2 kernel. Thus, the PID is always in CONTEXTIDR_EL2.

Sorry for confusion.  I'd like to rephrase as:

It's possible that the two bits ETM_OPT_CTXTID and ETM_OPT_CTXTID2 are
enabled at the same time when the session runs on an EL2 kernel.  This
means the CONTEXTIDR_EL1 and CONTEXTIDR_EL2 both will be recorded in
the trace data, the tool will selectively use CONTEXTIDR_EL2 as PID.

> > + */
> > +int cs_etm__get_pid_fmt(u8 trace_chan_id, u64 *pid_fmt)
> > +{
> > +	struct int_node *inode;
> > +	u64 *metadata, val;
> > +
> > +	inode = intlist__find(traceid_list, trace_chan_id);
> > +	if (!inode)
> > +		return -EINVAL;
> > +
> > +	metadata = inode->priv;
> > +
> > +	if (metadata[CS_ETM_MAGIC] == __perf_cs_etmv3_magic) {
> > +		val = metadata[CS_ETM_ETMCR];
> > +		/* CONTEXTIDR is traced */
> > +		if (val & BIT(ETM_OPT_CTXTID))
> > +			*pid_fmt = BIT(ETM_OPT_CTXTID);
> > +	} else {
> > +		val = metadata[CS_ETMV4_TRCCONFIGR];
> > +
> > +		*pid_fmt = 0;
> > +
> > +		/* CONTEXTIDR_EL2 is traced */
> > +		if (val & (BIT(ETM4_CFG_BIT_VMID) | BIT(ETM4_CFG_BIT_VMID_OPT)))
> > +			*pid_fmt = BIT(ETM_OPT_CTXTID2);
> > +
> > +		/* CONTEXTIDR_EL1 is traced */
> > +		if (val & BIT(ETM4_CFG_BIT_CTXTID))
> 
> I haven't looked at how this gets used. But, Shouldn't this be :
> 
> 		else if (val & BIT(ETM4_CFG_BIT_CTXTID)) ?

Actually it's deliberately to set both bits ETM_OPT_CTXTID2 and
ETM_OPT_CTXTID if user has enable configs "contextid1" and
"contextid2".  So this is exactly the reversed flow in the
function cs_etmv4_get_config().

Thanks,
Leo