On 23/10/2019 17:51, Marc Zyngier wrote:
> On 2019-10-23 04:22, Mao Wenan wrote:
>> If KVM=y, it will select SCHEDSTATS, below erros can
>> be seen:
>> kernel/sched/stats.h: In function rq_sched_info_arrive:
>> kernel/sched/stats.h:12:20: error: struct sched_info
>> has no member named run_delay
>> rq->rq_sched_info.run_delay += delta;
>> ^
>> kernel/sched/stats.h:13:20: error: struct sched_info
>> has no member named pcount
>> rq->rq_sched_info.pcount++;
>> ^
>> kernel/sched/stats.h: In function rq_sched_info_dequeued:
>> kernel/sched/stats.h:31:20: error: struct sched_info has
>> no member named run_delay
>> rq->rq_sched_info.run_delay += delta;
>>
>> These are because CONFIG_SCHED_INFO is not set, This patch
>> is to select SCHED_INFO before SCHEDSTATS.
>>
>> Fixes: 8564d6372a7d ("KVM: arm64: Support stolen time reporting via
>> shared structure")
>> Signed-off-by: Mao Wenan <maowenan@xxxxxxxxxx>
>> ---
>> arch/arm64/kvm/Kconfig | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
>> index d8b88e4..3c46eac 100644
>> --- a/arch/arm64/kvm/Kconfig
>> +++ b/arch/arm64/kvm/Kconfig
>> @@ -39,6 +39,7 @@ config KVM
>> select IRQ_BYPASS_MANAGER
>> select HAVE_KVM_IRQ_BYPASS
>> select HAVE_KVM_VCPU_RUN_PID_CHANGE
>> + select SCHED_INFO
>> select SCHEDSTATS
>> ---help---
>> Support hosting virtualized guest machines.
>
> SCHEDSTATS is really an odd choice. Here's what I get after disabling
> DEBUG_KERNEL (from defconfig):
>
> WARNING: unmet direct dependencies detected for SCHEDSTATS
> Depends on [n]: DEBUG_KERNEL [=n] && PROC_FS [=y]
> Selected by [y]:
> - KVM [=y] && VIRTUALIZATION [=y] && OF [=y]
>
> WARNING: unmet direct dependencies detected for SCHEDSTATS
> Depends on [n]: DEBUG_KERNEL [=n] && PROC_FS [=y]
> Selected by [y]:
> - KVM [=y] && VIRTUALIZATION [=y] && OF [=y]
>
> WARNING: unmet direct dependencies detected for SCHEDSTATS
> Depends on [n]: DEBUG_KERNEL [=n] && PROC_FS [=y]
> Selected by [y]:
> - KVM [=y] && VIRTUALIZATION [=y] && OF [=y]
>
> So clearly SCHEDSTATS isn't meant to be selected on its own.
>
> We can either just select SCHED_INFO (which *nobody else does*), or go
> the full x86 way which selects TASK_DELAY_ACCT (and thus depends on
> NET && MULTIUSER). My gut feeling is that we shouldn't deviate too much
> from x86...
>
> Thoughts?
I suspect you're right - TASK_DELAY_ACCT seems to be the closest to what
we need. SCHEDSTATS has the "advantage" of forcing sched_info_on() to
return true - preventing it from being disabled. But we clearly don't
want to require CONFIG_DEBUG_KERNEL for CONFIG_KVM.
The next best is CONFIG_TASK_DELAY_ACCT which enables sched_info_on()
unless "nodelayacct" is specified on the cmdline. It seems reasonable
that the cmdline option might break stolen time.
So let's just copy x86:
-----8<-----
>From 915893f5c57241cc29d90769b3f720a6135277d7 Mon Sep 17 00:00:00 2001
From: Steven Price <steven.price@xxxxxxx>
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@xxxxxxxxxx>
Fixes: 8564d6372a7d ("KVM: arm64: Support stolen time reporting via shared structure")
Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
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
--
2.20.1
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