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SubjectRe: [PATCH v4 04/10] coresight: etm-perf: update to handle configuration selection
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On 3/4/21 2:19 PM, Mike Leach wrote:
> Hi Suzuki,
>
> On Thu, 4 Mar 2021 at 12:13, Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>>
>> On 1/28/21 5:09 PM, Mike Leach wrote:
>>> Loaded coresight configurations are registered in the cs_etm\cs_config sub
>>> directory. This extends the etm-perf code to handle these registrations,
>>> and the cs_syscfg driver to perform the registration on load.
>>>
>>> Signed-off-by: Mike Leach <mike.leach@linaro.org>
>>> ---
>>> .../hwtracing/coresight/coresight-config.h | 5 +-
>>> .../hwtracing/coresight/coresight-etm-perf.c | 164 +++++++++++++++---
>>> .../hwtracing/coresight/coresight-etm-perf.h | 8 +
>>> .../hwtracing/coresight/coresight-syscfg.c | 13 +-
>>> 4 files changed, 166 insertions(+), 24 deletions(-)
>>>


>>> +static ssize_t etm_perf_cscfg_event_show(struct device *dev,
>>> + struct device_attribute *dattr,
>>> + char *buf)
>>> +{
>>> + struct dev_ext_attribute *ea;
>>> +
>>> + ea = container_of(dattr, struct dev_ext_attribute, attr);
>>> + return scnprintf(buf, PAGE_SIZE, "%s\n", (const char *)(ea->var));
>>> +}
>>
>> "configid=0x%lx", (unsigned long)ea->var ?
>>
>
> ea->var _is_ "configid=0x%lx" due to the way perf handles the events
> sub-dir entries.
>

This must be combined with the suggestion below.

>>> +
>>> +static int etm_perf_add_cscfg_event(struct device *dev, struct cscfg_config_desc *cs_cfg)
>>> +{
>>> + struct dev_ext_attribute *ea;
>>> + unsigned long hash;
>>> + int ret;
>>> + struct device *pmu_dev = etm_pmu.dev;
>>> +
>>> + ea = devm_kzalloc(dev, sizeof(*ea), GFP_KERNEL);
>>> + if (!ea)
>>> + return -ENOMEM;
>>> +
>>> + hash = (unsigned long)cs_cfg->id_ea->var;
>>> +
>>> + sysfs_attr_init(&ea->attr.attr);
>>> + ea->attr.attr.name = devm_kstrdup(dev, cs_cfg->name, GFP_KERNEL);
>>> + if (!ea->attr.attr.name)
>>> + return -ENOMEM;
>>> +
>>> + /*
>>> + * attribute value is "configid=<hash>".
>>> + * this will be what perf evaluates when the config name is used
>>> + * on the command line.
>>> + */
>>> + ea->var = devm_kzalloc(dev, CSCFG_EVENT_STR_SIZE, GFP_KERNEL);
>>> + if (!ea->var)
>>> + return -ENOMEM;
>>
>> Could we drop this string and use the "hash" instead ?
>>
>
> No. My understanding is that we have added an events directory to
> cs_etm, and add the configurations in there:-
>
> cs_etm/events/autofdo
>
> Now the contents of autofdo are "configid=0x<hash-value>" - where
> hash-value is the hash of "autofdo".
>
> On the perf command line:-
>
> perf record -e cs_etm/autofdo/ .....
>
> will result in perf parsing autofdo, looking in the events dir for
> cs_etm, seeing the configid=-string, and parsing that to assign to
> configid attribute - which we have allocated to config2:63:32 - this
> will then appear as a value in the perf_event and we can load the
> configuration when starting up the event on the ETM etc.

Sorry, I was not explicit in my comments. You could drop the string and
have ea->var = hash. And the _show() could simply do

"configid=0x%lx" , hash

as mentioned above.

That would avoid another string allocation, with the same interface.

Suzuki

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