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

[Yang Jialong 杨佳龙]

在 2024/2/27 2:57, Robin Murphy 写道:
> On 19/02/2024 6:37 am, Yang Jialong 杨佳龙 wrote:
> > 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@xxxxxxxxxxxx>
> > > > > ---
> > > > >   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).
>
> Now consider the other case below that, where "type" has not matched 
> anything registered, so "pmu" is NULL, and the event is then offered to 
> *every* registered PMU to see if anyone accepts it. Note that even CPU 
> PMUs don't always register as PERF_TYPE_RAW, and in particular arm_pmu 
> doesn't.
arm_pmu has flag PERF_PMU_CAP_EXTENDED_HW_TYPE.

From below command, we can say that generic events is related to the 
pmus with type PERF_TYPE_RAW.
~/real_kernel $ grep -nr "PERF_TYPE_HARDWARE" arch/ drivers/ |cut -d: 
-f1|xargs egrep -c "perf_pmu_register.*PERF_TYPE_RAW"
arch/alpha/kernel/perf_event.c:1
arch/alpha/kernel/perf_event.c:1
arch/arc/kernel/perf_event.c:1
arch/csky/kernel/perf_event.c:1
arch/loongarch/kernel/perf_event.c:1
arch/loongarch/kernel/perf_event.c:1
arch/mips/kernel/perf_event_mipsxx.c:1
arch/mips/kernel/perf_event_mipsxx.c:1
arch/powerpc/perf/8xx-pmu.c:1
arch/powerpc/perf/core-fsl-emb.c:1
arch/powerpc/perf/core-book3s.c:1
arch/riscv/kvm/vcpu_pmu.c:0
arch/s390/kernel/perf_cpum_sf.c:1
arch/s390/kernel/perf_cpum_cf.c:0
arch/s390/kernel/perf_cpum_cf.c:0
arch/s390/kernel/perf_cpum_cf.c:0
arch/s390/kernel/perf_cpum_cf.c:0
arch/sh/kernel/perf_event.c:1
arch/sh/kernel/perf_event.c:1
arch/sparc/kernel/perf_event.c:1
arch/x86/events/amd/ibs.c:0
arch/x86/events/intel/core.c:0
arch/x86/events/core.c:1
arch/xtensa/kernel/perf_event.c:1
drivers/perf/arm_pmu.c:0
drivers/perf/arm_pmu.c:0
drivers/perf/riscv_pmu.c:0
drivers/perf/riscv_pmu_legacy.c:1
drivers/perf/arm_pmuv3.c:0
drivers/perf/riscv_pmu_sbi.c:1

From this, we can say that generic events is related to the pmus with 
capability PERF_PMU_CAP_EXTENDED_HW_TYPE.
~/real_kernel $ grep -nr "PERF_TYPE_HARDWARE" arch/ drivers/ |cut -d: 
-f1|xargs grep -c "PERF_PMU_CAP_EXTENDED_HW_TYPE"
arch/alpha/kernel/perf_event.c:0
arch/alpha/kernel/perf_event.c:0
arch/arc/kernel/perf_event.c:0
arch/csky/kernel/perf_event.c:0
arch/loongarch/kernel/perf_event.c:0
arch/loongarch/kernel/perf_event.c:0
arch/mips/kernel/perf_event_mipsxx.c:0
arch/mips/kernel/perf_event_mipsxx.c:0
arch/powerpc/perf/8xx-pmu.c:0
arch/powerpc/perf/core-fsl-emb.c:0
arch/powerpc/perf/core-book3s.c:0
arch/riscv/kvm/vcpu_pmu.c:0
arch/s390/kernel/perf_cpum_sf.c:0
arch/s390/kernel/perf_cpum_cf.c:0
arch/s390/kernel/perf_cpum_cf.c:0
arch/s390/kernel/perf_cpum_cf.c:0
arch/s390/kernel/perf_cpum_cf.c:0
arch/sh/kernel/perf_event.c:0
arch/sh/kernel/perf_event.c:0
arch/sparc/kernel/perf_event.c:0
arch/x86/events/amd/ibs.c:0
arch/x86/events/intel/core.c:0
arch/x86/events/core.c:1
arch/xtensa/kernel/perf_event.c:0
drivers/perf/arm_pmu.c:2
drivers/perf/arm_pmu.c:2
drivers/perf/riscv_pmu.c:0
drivers/perf/riscv_pmu_legacy.c:0
drivers/perf/arm_pmuv3.c:0
drivers/perf/riscv_pmu_sbi.c:0

****************************
Something bad belows:
~/real_kernel $ grep -nr "PERF_TYPE_HARDWARE" arch/ drivers/ |cut -d: 
-f1|xargs egrep -c "perf_pmu_register.*-1"
arch/alpha/kernel/perf_event.c:0
arch/alpha/kernel/perf_event.c:0
arch/arc/kernel/perf_event.c:0
arch/csky/kernel/perf_event.c:0
arch/loongarch/kernel/perf_event.c:0
arch/loongarch/kernel/perf_event.c:0
arch/mips/kernel/perf_event_mipsxx.c:0
arch/mips/kernel/perf_event_mipsxx.c:0
arch/powerpc/perf/8xx-pmu.c:0
arch/powerpc/perf/core-fsl-emb.c:0
arch/powerpc/perf/core-book3s.c:0
arch/riscv/kvm/vcpu_pmu.c:0
arch/s390/kernel/perf_cpum_sf.c:0
arch/s390/kernel/perf_cpum_cf.c:2
arch/s390/kernel/perf_cpum_cf.c:2
arch/s390/kernel/perf_cpum_cf.c:2
arch/s390/kernel/perf_cpum_cf.c:2
arch/sh/kernel/perf_event.c:0
arch/sh/kernel/perf_event.c:0
arch/sparc/kernel/perf_event.c:0
arch/x86/events/amd/ibs.c:1
arch/x86/events/intel/core.c:0
arch/x86/events/core.c:0
arch/xtensa/kernel/perf_event.c:0
drivers/perf/arm_pmu.c:1
drivers/perf/arm_pmu.c:1
drivers/perf/riscv_pmu.c:0
drivers/perf/riscv_pmu_legacy.c:0
drivers/perf/arm_pmuv3.c:0
drivers/perf/riscv_pmu_sbi.c:0
The pmus::event_init handled PERF_TYPE_HARDWARE, but they was registered 
with perf_pmu_register(*, *, -1) without CAP_EXTENDED_HW_TPYE.

Can we unify them with PERF_TYPE_RAW or CAP_EXTENDED_HW_TYPE? Maybe the 
latter is well. So we can assign idr PERF_TYPE_HARDWARE and 
PERF_TYPE_HW_CACHE a known pmu in perf_pmu_register just like:
if(is_support_generic(pmu)) {
	ret = idr_alloc(&pmu_idr, pmu, PERF_TYPE_HARDWAR, PERF_TYPE_HARDWARE + 
1, GFP_KERNEL);
	if(ret < 0)
		goto free_pdc;
	ret = idr_alloc(&pmu_idr, pmu, PERF_TYPE_HW_CACHE, PERF_TYPE_HW_CACHE + 
1, GFP_KERNEL);
	if(ret < 0)
		goto free_pdc;
}
We will has a easy and rational way to write code in 
core.c::perf_init_event and perf_try_init_event about generic events. We 
can judge cpu < 0 in perf_try_init_event for uncore pmus.
> Thanks,
> Robin.