linux-kernel - Re: [PATCH RFC 1/8] perf/core: Add *group_leader to perf_event_create_kernel

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Message-ID: <e8278857-1d30-877a-5c8d-329d3cba755b@gmail.com>
Date:   Thu, 15 Dec 2022 21:11:32 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Fenghua Yu <fenghua.yu@...el.com>, kvmarm@...ts.linux.dev,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH RFC 1/8] perf/core: Add *group_leader to
 perf_event_create_kernel_counter()

On 12/12/2022 9:23 pm, Marc Zyngier wrote:
> On Mon, 12 Dec 2022 12:58:37 +0000,
> Like Xu <like.xu.linux@...il.com> wrote:
>>
>> From: Like Xu <likexu@...cent.com>
>>
>> Like syscalls users, kernel-space perf_event creators may also use group
>> counters abstraction to gain pmu functionalities, and an in-kernel counter
>> groups behave much like normal 'single' counters, following the group
>> semantics-based behavior.
>>
>> No functional changes at this time. An example will be that KVM creates
>> Intel slot event as group leader and other topdown metric events to emulate
>> MSR_PERF_METRICS pmu capability for guests.
>>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Marc Zyngier <maz@...nel.org>
>> Cc: Fenghua Yu <fenghua.yu@...el.com>
>> Cc: kvmarm@...ts.linux.dev
>> Cc: linux-perf-users@...r.kernel.org
>> Signed-off-by: Like Xu <likexu@...cent.com>
>> ---
>>   arch/arm64/kvm/pmu-emul.c                 | 4 ++--
>>   arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 4 ++--
>>   arch/x86/kvm/pmu.c                        | 2 +-
>>   arch/x86/kvm/vmx/pmu_intel.c              | 2 +-
>>   include/linux/perf_event.h                | 1 +
>>   kernel/events/core.c                      | 4 +++-
>>   kernel/events/hw_breakpoint.c             | 4 ++--
>>   kernel/events/hw_breakpoint_test.c        | 2 +-
>>   kernel/watchdog_hld.c                     | 2 +-
>>   9 files changed, 14 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
>> index 24908400e190..11c3386bc86b 100644
>> --- a/arch/arm64/kvm/pmu-emul.c
>> +++ b/arch/arm64/kvm/pmu-emul.c
>> @@ -624,7 +624,7 @@ static void kvm_pmu_create_perf_event(struct kvm_pmc *pmc)
>>   
>>   	attr.sample_period = compute_period(pmc, kvm_pmu_get_pmc_value(pmc));
>>   
>> -	event = perf_event_create_kernel_counter(&attr, -1, current,
>> +	event = perf_event_create_kernel_counter(&attr, -1, current, NULL,
>>   						 kvm_pmu_perf_overflow, pmc);
> 
> Wouldn't it be better to have a separate helper that takes the group leader
> as a parameter, and reimplement perf_event_create_kernel_counter() in term
> of this helper?
> 
> 	M.
> 

Applied. It makes changes more concise, thank you.