linux-kernel - Re: [PATCH v2 1/9] perf: Add EVENT_ATTR

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Date:   Wed, 2 Jun 2021 16:45:23 +0800
From:   "liuqi (BA)" <liuqi115@...wei.com>
To:     Will Deacon <will@...nel.org>, Qi Liu <liuqi115@...wei.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH v2 1/9] perf: Add EVENT_ATTR_ID to simplify event
 attributes


Hi Will,

Thanks for reviewing this patch.

On 2021/6/1 21:10, Will Deacon wrote:
> On Wed, May 19, 2021 at 05:51:51PM +0800, Qi Liu wrote:
>> Similar EVENT_ATTR macros are defined in many PMU drivers,
>> like HiSilicon PMU driver, Arm PMU driver, Arm SMMU PMU
>> driver. So Add a generic macro to simplify code.
>>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
>> Signed-off-by: Qi Liu <liuqi115@...wei.com>
>> ---
>>   include/linux/perf_event.h | 6 ++++++
>>   kernel/events/core.c       | 2 ++
>>   2 files changed, 8 insertions(+)
>>
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index f5a6a2f..d0aa74e 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -1576,6 +1576,12 @@ static struct perf_pmu_events_attr _var = {				    \
>>   	.event_str	= _str,						    \
>>   };
>>   
>> +#define PMU_EVENT_ATTR_ID(_name, _id)					     \
>> +	(&((struct perf_pmu_events_attr[]) {				     \
>> +		{ .attr = __ATTR(_name, 0444, perf_event_sysfs_show, NULL),  \
>> +		  .id = _id, }						     \
>> +	})[0].attr.attr)
>> +
>>   #define PMU_FORMAT_ATTR(_name, _format)					\
>>   static ssize_t								\
>>   _name##_show(struct device *dev,					\
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 0ac818b..330d9cc 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -13295,6 +13295,8 @@ ssize_t perf_event_sysfs_show(struct device *dev, struct device_attribute *attr,
>>   
>>   	if (pmu_attr->event_str)
>>   		return sprintf(page, "%s\n", pmu_attr->event_str);
>> +	else
>> +		return sprintf(page, "config=%#llx\n", pmu_attr->id);
> 
> I think it's a really bad idea to hardcode this here. For example, I think
> this patch series breaks user ABI for the SMMU PMU which used to print:
> 
> 	"event=0x%02llx\n"
> 
> and by the looks of it many of the other conversions are unsound too.
> 
Got it, so I'll use pmu_attr->event_str here, for example,
SMMU_EVENT_ATTR(cycles, "event=0x00")

As PMU_EVENT_ATTR_STRING is already defined in linux/perf_event.h，and is 
used in drivers of multi architectures, add a new common macro might be 
better than modify PMU_EVENT_ATTR_STRING.
Do you have any suggestion about the name of new common macro?

Thanks,
Qi
> I'm all for a common macro, but the string needs to be determined by the
> driver.
> 
> Will
> .
>