linux-kernel - Re: [PATCH RFC 5/7] perf pmu: Support matching by sysid

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Date:   Tue, 11 Feb 2020 15:07:31 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
        <namhyung@...nel.org>, <will@...nel.org>, <ak@...ux.intel.com>,
        <linuxarm@...wei.com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <suzuki.poulose@....com>,
        <james.clark@....com>, <zhangshaokun@...ilicon.com>,
        <robin.murphy@....com>
Subject: Re: [PATCH RFC 5/7] perf pmu: Support matching by sysid

On 11/02/2020 13:47, Jiri Olsa wrote:

Hi Jirka,

>>>> +
>>>> +	return buf;
>>>> +}
>>>> +
>>
>> I have another series to add kernel support for a system identifier sysfs
>> entry, which I sent after this series:
>>
>> https://lore.kernel.org/linux-acpi/1580210059-199540-1-git-send-email-john.garry@huawei.com/
>>
>> It is different to what I am relying on here - it uses a kernel soc driver
>> for firmware ACPI PPTT identifier. Progress is somewhat blocked at the
>> moment however and I may have to use a different method:
>>
>> https://lore.kernel.org/linux-acpi/20200128123415.GB36168@bogus/
> 
> I'll try to check ;-)

Summary is that there exists an ACPI firmware field which we could 
expose to userspace via sysfs - this would provide the system id. 
However there is a proposal to deprecate it in the ACPI standard and, as 
such, would prefer that we don't add kernel support for it at this stage.

So I am evaluating the alternative in the meantime, which again is some 
firmware method which should allow us to expose a system id to userspace 
via sysfs. Unfortunately this is arm specific. However, other archs can 
still provide their own method, maybe a soc driver:

Documentation/ABI/testing/sysfs-devices-soc#n15

> 
>>
>>>> +static char *perf_pmu__getsysid(void)
>>>> +{
>>>> +	char *sysid;
>>>> +	static bool printed;
>>>> +
>>>> +	sysid = getenv("PERF_SYSID");
>>>> +	if (sysid)
>>>> +		sysid = strdup(sysid);
>>>> +
>>>> +	if (!sysid)
>>>> +		sysid = get_sysid_str();
>>>> +	if (!sysid)
>>>> +		return NULL;
>>>> +
>>>> +	if (!printed) {
>>>> +		pr_debug("Using SYSID %s\n", sysid);
>>>> +		printed = true;
>>>> +	}
>>>> +	return sysid;
>>>> +}
>>>
>>> this part is getting complicated and AFAIK we have no tests for it
>>>
>>> if you could think of any tests that'd be great.. Perhaps we could
>>> load 'our' json test files and check appropriate events/aliasses
>>> via in pmu object.. or via parse_events interface.. those test aliases
>>> would have to be part of perf, but we have tests compiled in anyway
>>
>> Sorry, I don't fully follow.
>>
>> Are you suggesting that we could load the specific JSONs tables for a system
>> from the host filesystem?
> 
> I wish to see some test for all this.. I can only think about having
> 'test' json files compiled with perf and 'perf test' that looks them
> up and checks that all is in the proper place

OK, let me consider this part for perf test support.

Thanks,
John