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

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Message-ID: <a8116024-76df-4c42-15ef-de3f02436b8c@arm.com>
Date:   Thu, 4 Feb 2021 10:57:06 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Leo Yan <leo.yan@...aro.org>
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, Al Grant <al.grant@....com>
Subject: Re: [PATCH v2 6/7] perf cs-etm: Detect pid in VMID for kernel running
 at EL2

On 2/4/21 4:00 AM, Leo Yan wrote:
> 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@....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 CONTEXTIDR (Arm32)
>>> or CONTEXTIDR_EL1 (Arm64) is invalid but we have a valid VMID.
>>>
>>> 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 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@...aro.org>
>>>     */
>>> +#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".

No problem.

> 
>>
>>> +		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?

I have responded to the comment in the patch.

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


Thanks
Suzuki