Re: [PATCH v2 6/7] perf cs-etm: Detect pid in VMID for kernel running at EL2

[Leo Yan]

On Tue, Feb 02, 2021 at 11:29:47PM +0000, Suzuki Kuruppassery Poulose wrote:
> On 2/2/21 4:38 PM, Leo Yan wrote:
> > From: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > 
> > 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 CONTEXTIDR (Arm32)
> > or CONTEXTIDR_EL1 (Arm64) is invalid but we have a valid VMID.
> > 
> > Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > Cc: Al Grant <al.grant@xxxxxxx>
> > Co-developed-by: Leo Yan <leo.yan@xxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> > ---
> >   .../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 3f4bc4050477..fb2a163ff74e 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@xxxxxxxxxx>
> >    */
> > +#include <linux/coresight-pmu.h>
> >   #include <linux/err.h>
> >   #include <linux/list.h>
> >   #include <linux/zalloc.h>
> > @@ -491,13 +492,36 @@ 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)
> 
> Is this something we can cache in this function ? e.g,
> 	static u64 pid_fmt;
> 
> 	if (!pid_pfmt)
> 		ret = cs_etm__get_pid_fmt(trace_chan_id, &pid_fmt);
> 
> As all the ETMs will be running at the same exception level.

Sorry that I let you repeated your comments again.

To be honest, I considered this after read your comment in the previous
series, but I thought it's possible that multiple CPUs have different
PID format, especially for big.LITTLE arch.  After read your suggestion
again, I think my concern is not valid, even for big.LITTLE, all CPUs
should run on the same kernel exception level.

So will follow up your suggestion to cache "pid_fmt".

> 
> > +		return OCSD_RESP_FATAL_SYS_ERR;
> > +
> > +	/*
> > +	 * Process the PE_CONTEXT packets if we have a valid contextID or VMID.
> > +	 * If the kernel is running at EL2, the PID is traced in CONTEXTIDR_EL2
> > +	 * as VMID, Bit ETM_OPT_CTXTID2 is set in this case.
> > +	 */
> > +	switch (pid_fmt) {
> > +	case BIT(ETM_OPT_CTXTID):
> > +		if (elem->context.ctxt_id_valid)
> > +			tid = elem->context.context_id;
> > +		break;
> > +	case BIT(ETM_OPT_CTXTID2) | BIT(ETM_OPT_CTXTID):
> 
> I would rather fix the cs_etm__get_pid_fmt() to return either of these
> as commented. i.e, ETM_OPT_CTXTID or ETM_OPT_CTXTID2. Thus we don't
> need the this case.

I explained why I set both bits for ETM_OPT_CTXTID and ETM_OPT_CTXTID2
in the patch 05/07.  Could you take a look for it?

> With the above two addressed:
> 
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

Thanks,
Leo