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SubjectRe: [PATCH v2 5/7] perf cs-etm: Add helper cs_etm__get_pid_fmt()
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On 2/4/21 3:47 AM, Leo Yan wrote:
> 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().

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.

Cheers
Suzuki

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