linux-kernel - Re: [PATCH] perf/arm_smmuv3: Omit the two judgements which done in framework

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Date: Fri, 9 Feb 2024 16:32:00 +0000
From: Robin Murphy <robin.murphy@....com>
To: Will Deacon <will@...nel.org>, "JiaLong.Yang" <jialong.yang@...ngroup.cn>
Cc: Mark Rutland <mark.rutland@....com>, shenghui.qu@...ngroup.cn,
 ke.zhao@...ngroup.cn, zhijie.ren@...ngroup.cn,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/arm_smmuv3: Omit the two judgements which done in
 framework

On 2024-02-09 4:09 pm, Will Deacon wrote:
> On Thu, Dec 21, 2023 at 05:38:01PM +0800, JiaLong.Yang wrote:
>> 'event->attr.type != event->pmu->type' has been done in
>> core.c::perf_init_event() ,core.c::perf_event_modify_attr(), etc.
>>
>> This PMU is an uncore one. The core framework has disallowed
>> uncore-task events. So the judgement to event->cpu < 0 is no mean.
> 
> It would be great to refer to the changes which added those checks to
> the perf core code. From reading the code myself, I can't convince myself
> that perf_try_init_event() won't call into the driver.
> 
>>
>> The two judgements have been done in kernel/events/core.c
>>
>> Signed-off-by: JiaLong.Yang <jialong.yang@...ngroup.cn>
>> ---
>>   drivers/perf/arm_smmuv3_pmu.c | 8 --------
>>   1 file changed, 8 deletions(-)
> 
> It looks like _many_ perf drivers have these checks, so if they really
> aren't needed, we can clean this up bveyond SMMU. However, as I said
> above, I'm not quite convinced we can drop them.

Right, I think the logic prevents events with a specific PMU type being 
offered to other PMUs, but as far as I'm aware doesn't apply the other 
way round to stop generic events (PERF_TYPE_HARDWARE etc.) being offered 
to all PMUs, so it's those that system PMUs need to reject.

It's been on my wishlist for a long time to have a capability flag to 
say "I don't handle generic events, please only ever give me events of 
my exact type" so we *can* truly factor this into the core.

Thanks,
Robin.