linux-kernel - Re: [PATCH v4 4/5] hwtracing: hisi_ptt: Advertise PERF_PMU_CAP_NO

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Message-ID: <e3424908-a6a3-63f7-f3b7-e10b00cdfd13@huawei.com>
Date:   Tue, 20 Jun 2023 17:09:46 +0800
From:   Yicong Yang <yangyicong@...wei.com>
To:     hejunhao <hejunhao3@...wei.com>, <mathieu.poirier@...aro.org>,
        <suzuki.poulose@....com>, <jonathan.cameron@...wei.com>,
        <corbet@....net>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>
CC:     <yangyicong@...ilicon.com>, <alexander.shishkin@...ux.intel.com>,
        <helgaas@...nel.org>, <linux-pci@...r.kernel.org>,
        <prime.zeng@...wei.com>
Subject: Re: [PATCH v4 4/5] hwtracing: hisi_ptt: Advertise
 PERF_PMU_CAP_NO_EXCLUDE for PTT PMU

Hi Junhao,

On 2023/6/19 21:00, hejunhao wrote:
> Hi, Yicong
> 
> 
> On 2023/6/6 22:22, Yicong Yang wrote:
>> From: Yicong Yang <yangyicong@...ilicon.com>
>>
>> The PTT trace collects PCIe TLP headers from the PCIe link and don't
>> have the ability to exclude certain context. It doesn't support itrace
>> as well. So only advertise PERF_PMU_CAP_NO_EXCLUDE. This will greatly
>> save the storage of final data. Tested tracing idle link for ~15s,
>> without this patch we'll collect ~28.682MB data for context related
>> information and with this patch it reduced to ~0.226MB.
>>
>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
>> ---
>>   drivers/hwtracing/ptt/hisi_ptt.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/hwtracing/ptt/hisi_ptt.c b/drivers/hwtracing/ptt/hisi_ptt.c
>> index 5c7e93e7705f..ff2c16efe5b1 100644
>> --- a/drivers/hwtracing/ptt/hisi_ptt.c
>> +++ b/drivers/hwtracing/ptt/hisi_ptt.c
>> @@ -1210,7 +1210,7 @@ static int hisi_ptt_register_pmu(struct hisi_ptt *hisi_ptt)
>>         hisi_ptt->hisi_ptt_pmu = (struct pmu) {
>>           .module        = THIS_MODULE,
>> -        .capabilities    = PERF_PMU_CAP_EXCLUSIVE | PERF_PMU_CAP_ITRACE,
>> +        .capabilities    = PERF_PMU_CAP_NO_EXCLUDE,
> 
> According to the error prompt of function hisi_ptt_trace_start().
> https://elixir.bootlin.com/linux/v6.4-rc7/source/drivers/hwtracing/ptt/hisi_ptt.c#L197
> 
> You may be need to keep advertise PERF_PMU_CAP_EXCLUSIVE?
> Such pmus can only have one event scheduled at a time, if not the perf
> tool will report device busy.
> 

Thanks for point it out. Checking [1] I think we still need this flag here, will add
it back.

[1] https://github.com/torvalds/linux/blob/v6.4-rc6/kernel/events/core.c#L5054

Thanks.