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SubjectRe: [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@linaro.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
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