linux-kernel - Re: [PATCH 4/6] kvm: Select SCHED_INFO instead of TASK_DELAY

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Date:   Wed, 5 May 2021 13:37:12 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de,
        mingo@...nel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, bsingharora@...il.com, maz@...nel.org
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        riel@...riel.com, hannes@...xchg.org
Subject: Re: [PATCH 4/6] kvm: Select SCHED_INFO instead of TASK_DELAY_ACCT

On 05/05/21 12:59, Peter Zijlstra wrote:
> AFAICT KVM only relies on SCHED_INFO. Nothing uses the p->delays data
> that belongs to TASK_DELAY_ACCT.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Right, SCHED_INFO didn't exist at the time (it was introduced in 2015, 
while KVM started using run_delay in 2011).  I'm not sure if it could 
have used SCHEDSTATS instead.

Acked-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo

> ---
>   arch/arm64/kvm/Kconfig |    5 +----
>   arch/x86/kvm/Kconfig   |    5 +----
>   2 files changed, 2 insertions(+), 8 deletions(-)
> 
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -20,8 +20,6 @@ if VIRTUALIZATION
>   menuconfig KVM
>   	bool "Kernel-based Virtual Machine (KVM) support"
>   	depends on OF
> -	# for TASKSTATS/TASK_DELAY_ACCT:
> -	depends on NET && MULTIUSER
>   	select MMU_NOTIFIER
>   	select PREEMPT_NOTIFIERS
>   	select HAVE_KVM_CPU_RELAX_INTERCEPT
> @@ -38,8 +36,7 @@ menuconfig KVM
>   	select IRQ_BYPASS_MANAGER
>   	select HAVE_KVM_IRQ_BYPASS
>   	select HAVE_KVM_VCPU_RUN_PID_CHANGE
> -	select TASKSTATS
> -	select TASK_DELAY_ACCT
> +	select SCHED_INFO
>   	help
>   	  Support hosting virtualized guest machines.
>   
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -22,8 +22,6 @@ config KVM
>   	tristate "Kernel-based Virtual Machine (KVM) support"
>   	depends on HAVE_KVM
>   	depends on HIGH_RES_TIMERS
> -	# for TASKSTATS/TASK_DELAY_ACCT:
> -	depends on NET && MULTIUSER
>   	depends on X86_LOCAL_APIC
>   	select PREEMPT_NOTIFIERS
>   	select MMU_NOTIFIER
> @@ -36,8 +34,7 @@ config KVM
>   	select KVM_ASYNC_PF
>   	select USER_RETURN_NOTIFIER
>   	select KVM_MMIO
> -	select TASKSTATS
> -	select TASK_DELAY_ACCT
> +	select SCHED_INFO
>   	select PERF_EVENTS
>   	select HAVE_KVM_MSI
>   	select HAVE_KVM_CPU_RELAX_INTERCEPT
> 
>