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

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Message-ID: <20210204112349.GB4737@leoy-ThinkPad-X240s>
Date:   Thu, 4 Feb 2021 19:23:49 +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 Thu, Feb 04, 2021 at 10:54:24AM +0000, Suzuki Kuruppassery Poulose wrote:

[...]

> > > > +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().
> 
> The point is, we don't care if the user selected both options. What we
> care is, where can we find the PID. CONTEXTIDR_EL1 or CONTEXTIDR_EL2.
> As such, get_pid_fmt simply should make that decision and pass it on.
> So, if the CONTEXTIDR_EL2 is selected (which can only be done successfully
> on an EL2 kernel), thats our pid.
> 
> So we should return the format for the PID here. i.e
>  ETM_OPT_CTXTID2 OR ETM_OPT_CTXTID. But not both.

Okay, if so I will follow your suggestion.

Thanks,
Leo