Re: [PATCH 3/3] rfc: perf: cs_etm: Detect pid in VMID for kernel running at EL2

From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: linux-arm-kernel@lists.infradead.org, Mike Leach <mike.leach@linaro.org>
Cc: al.grant@arm.com, mathieu.poirier@linaro.org,
	anshuman.khandual@arm.com, coresight@lists.linaro.org,
	leo.yan@linaro.org, mike.leach@linaro.org
Subject: Re: [PATCH 3/3] rfc: perf: cs_etm: Detect pid in VMID for kernel running at EL2
Date: Tue, 10 Nov 2020 22:57:05 +0000	[thread overview]
Message-ID: <a3e237a0-a22f-4379-b48a-6b53420017d7@arm.com> (raw)
In-Reply-To: <20201110183313.1823760-4-suzuki.poulose@arm.com>

Mike,

Related to this patch, I have a question about the print decoder
in OpenCSD. Withe TRCCONFIGR.VMIDOPT, we have CONTEXTIDR_EL2 in
VMID instead of the real VMID. Does it make sense to change the
print decoder to reflect this in the o/p ?

i.e, instead of :

Idx:530; ID:14; I_ADDR_CTXT_L_64IS0 .. Ctxt: AArch64,EL0, NS; VMID=0xAA;

Could this be

Idx:530; ID:14; I_ADDR_CTXT_L_64IS0 .. Ctxt: AArch64,EL0, NS; CID2=0xAA;

with VMIDOPT ?

I understand it is a bit naive, and there are widespread users of
OpenCSD and it could potentially break any existing users. But worth
checking.

Cheers
Suzuki

On 11/10/20 6:33 PM, Suzuki K Poulose wrote:
> 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.
> 
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> 
> Ideally, we should also confirm that the VMID_OPT is also set
> in the trcconfigr for choosing the VMID. Hence the RFC. May be
> that is something we could cache in the "decoder" instance ?
> ---
>   .../perf/util/cs-etm-decoder/cs-etm-decoder.c | 28 +++++++++++--------
>   1 file changed, 17 insertions(+), 11 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..31ba7ff57914 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> @@ -502,19 +502,25 @@ cs_etm_decoder__set_tid(struct cs_etm_queue *etmq,
>   {
>   	pid_t tid;
>   
> -	/* Ignore PE_CONTEXT packets that don't have a valid contextID */
> -	if (!elem->context.ctxt_id_valid)
> -		return OCSD_RESP_CONT;
> -
> -	tid =  elem->context.context_id;
> -	if (cs_etm__etmq_set_tid(etmq, tid, trace_chan_id))
> -		return OCSD_RESP_FATAL_SYS_ERR;
> -
>   	/*
> -	 * A timestamp is generated after a PE_CONTEXT element so make sure
> -	 * to rely on that coming one.
> +	 * 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.
>   	 */
> -	cs_etm_decoder__reset_timestamp(packet_queue);
> +	if (elem->context.ctxt_id_valid || elem->context.vmid_valid) {
> +		if (elem->context.ctxt_id_valid)
> +			tid =  elem->context.context_id;
> +		else
> +			tid = elem->context.vmid;
> +		if (cs_etm__etmq_set_tid(etmq, tid, trace_chan_id))
> +			return OCSD_RESP_FATAL_SYS_ERR;
> +		/*
> +		 * A timestamp is generated after a PE_CONTEXT element so make sure
> +		 * to rely on that coming one.
> +		 */
> +		cs_etm_decoder__reset_timestamp(packet_queue);
> +	}
>   
>   	return OCSD_RESP_CONT;
>   }
> 

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