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

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Message-ID: <840C2556C7DDB57C+c4575f04-5d1b-44a5-8f7b-3a2ba1fd61c4@shingroup.cn>
Date: Mon, 19 Feb 2024 14:37:08 +0800
From: Yang Jialong 杨佳龙 <jialong.yang@...ngroup.cn>
To: Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>
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



在 2024/2/10 0:32, Robin Murphy 写道:
> 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.


It's core framework's responsible to differ generic events and others, 
or uncore pmu and core pmu.
Here we have flag PERF_TYPE_HARDWARE, PERF_TYPE_HW_CACHE, 
PERF_PMU_CAP_EXTENDED_HW_TYPE doing this.

again:
         rcu_read_lock();
         pmu = idr_find(&pmu_idr, type);
         rcu_read_unlock();
         if (pmu) {
                 if (event->attr.type != type && type != PERF_TYPE_RAW &&
                     !(pmu->capabilities & PERF_PMU_CAP_EXTENDED_HW_TYPE))
                         goto fail; /* generic event with no ability pmu */
This can avoid driver code (event->attr.type != event->pmu->type).

And, code:
if (pmu->task_ctx_nr == perf_invalid_context && (task || cgroup_fd != -1)) {
	err = -EINVAL;
	goto err_pmu;
}
can promise not uncore-task event.

We should confirm that uncore event should be cpu >= 0.

> 
> Thanks,
> Robin.
>