linux-kernel - Re: [PATCH] KVM: arm64: Select SCHED

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Date:   Thu, 24 Oct 2019 14:19:08 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Steven Price <steven.price@....com>
Cc:     Mao Wenan <maowenan@...wei.com>, <catalin.marinas@....com>,
        <kernel-janitors@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <will@...nel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] KVM: arm64: Select SCHED_INFO before SCHEDSTATS

On 2019-10-24 12:22, Steven Price wrote:

[...]

> From 915893f5c57241cc29d90769b3f720a6135277d7 Mon Sep 17 00:00:00 
> 2001
> From: Steven Price <steven.price@....com>
> Date: Thu, 24 Oct 2019 12:14:36 +0100
> Subject: [PATCH] KVM: arm64: Select TASK_DELAY_ACCT rather than 
> SCHEDSTATS
>
> SCHEDSTATS requires DEBUG_KERNEL (and PROC_FS) and therefore isn't a
> good choice for enabling the scheduling statistics required for 
> stolen
> time.
>
> Instead match the x86 configuration and select TASK_DELAY_ACCT. This
> adds the dependencies of NET && MULTIUSER for arm64 KVM.
>
> Suggested-by: Marc Zyngier <maz@...nel.org>
> Fixes: 8564d6372a7d ("KVM: arm64: Support stolen time reporting via
> shared structure")
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  arch/arm64/kvm/Kconfig | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index d8b88e40d223..1ffb300e2d92 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -21,6 +21,8 @@ if VIRTUALIZATION
>  config 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
> @@ -39,7 +41,7 @@ config KVM
>  	select IRQ_BYPASS_MANAGER
>  	select HAVE_KVM_IRQ_BYPASS
>  	select HAVE_KVM_VCPU_RUN_PID_CHANGE
> -	select SCHEDSTATS
> +	select TASK_DELAY_ACCT
>  	---help---
>  	  Support hosting virtualized guest machines.
>  	  We don't support KVM with 16K page tables yet, due to the 
> multiple

Same issue as before: you have an implicit config symbol selection.
TASK_DELAY_ACCT depends on TASKSTATS (which is why you have this NET &&
MULTIUSER constraint).

You need to select both TASK_DELAY_ACCT and TASKSTATS, as the comment 
you
add suggests.

         M.
-- 
Jazz is not dead. It just smells funny...