From: Marc Zyngier <maz@kernel.org>
To: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Joel Fernandes <joelaf@google.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Suleiman Souhlal <suleiman@google.com>,
Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support
Date: Wed, 21 Jul 2021 12:08:18 +0100 [thread overview]
Message-ID: <87a6mf3owt.wl-maz@kernel.org> (raw)
In-Reply-To: <YPf5MFV99zPdTu/U@google.com>
On Wed, 21 Jul 2021 11:38:40 +0100,
Sergey Senozhatsky <senozhatsky@chromium.org> wrote:
>
> On (21/07/21 09:40), Marc Zyngier wrote:
> > >
> > > Can that be cured by just checking vcpu->preempted before calling
> > > kvm_update_vcpu_preempted() ?
> >
> > It isn't obvious to me that this is the right thing to do.
> > vcpu->preempted is always updated on sched-out from the preempt
> > notifier if the vcpu was on the run-queue, so my guess is that it will
> > always be set when switching to another task.
> >
> > What you probably want is to check whether the vcpu is blocked by
> > introspecting the wait-queue with:
> >
> > scuwait_active(kvm_arch_vcpu_get_wait(vcpu)
> >
> > which will tell you whether you are blocking or not. We are already
> > using a similar construct for arming a background timer in this case.
>
> Can we examine if vcpu->run->exit_reason == WFE/WFI and avoid setting
> preempted state if so?
We never go back to userspace for WFI/WFE, so no reason to populate
the run structure.
Checking for the blocked state is the right thing to do, and we
already have the primitive for this. Just use it.
M.
--
Without deviation from the norm, progress is not possible.
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Joel Fernandes <joelaf@google.com>, Will Deacon <will@kernel.org>,
Suleiman Souhlal <suleiman@google.com>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support
Date: Wed, 21 Jul 2021 12:08:18 +0100 [thread overview]
Message-ID: <87a6mf3owt.wl-maz@kernel.org> (raw)
In-Reply-To: <YPf5MFV99zPdTu/U@google.com>
On Wed, 21 Jul 2021 11:38:40 +0100,
Sergey Senozhatsky <senozhatsky@chromium.org> wrote:
>
> On (21/07/21 09:40), Marc Zyngier wrote:
> > >
> > > Can that be cured by just checking vcpu->preempted before calling
> > > kvm_update_vcpu_preempted() ?
> >
> > It isn't obvious to me that this is the right thing to do.
> > vcpu->preempted is always updated on sched-out from the preempt
> > notifier if the vcpu was on the run-queue, so my guess is that it will
> > always be set when switching to another task.
> >
> > What you probably want is to check whether the vcpu is blocked by
> > introspecting the wait-queue with:
> >
> > scuwait_active(kvm_arch_vcpu_get_wait(vcpu)
> >
> > which will tell you whether you are blocking or not. We are already
> > using a similar construct for arming a background timer in this case.
>
> Can we examine if vcpu->run->exit_reason == WFE/WFI and avoid setting
> preempted state if so?
We never go back to userspace for WFI/WFE, so no reason to populate
the run structure.
Checking for the blocked state is the right thing to do, and we
already have the primitive for this. Just use it.
M.
--
Without deviation from the norm, progress is not possible.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Joel Fernandes <joelaf@google.com>, Will Deacon <will@kernel.org>,
Suleiman Souhlal <suleiman@google.com>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support
Date: Wed, 21 Jul 2021 12:08:18 +0100 [thread overview]
Message-ID: <87a6mf3owt.wl-maz@kernel.org> (raw)
In-Reply-To: <YPf5MFV99zPdTu/U@google.com>
On Wed, 21 Jul 2021 11:38:40 +0100,
Sergey Senozhatsky <senozhatsky@chromium.org> wrote:
>
> On (21/07/21 09:40), Marc Zyngier wrote:
> > >
> > > Can that be cured by just checking vcpu->preempted before calling
> > > kvm_update_vcpu_preempted() ?
> >
> > It isn't obvious to me that this is the right thing to do.
> > vcpu->preempted is always updated on sched-out from the preempt
> > notifier if the vcpu was on the run-queue, so my guess is that it will
> > always be set when switching to another task.
> >
> > What you probably want is to check whether the vcpu is blocked by
> > introspecting the wait-queue with:
> >
> > scuwait_active(kvm_arch_vcpu_get_wait(vcpu)
> >
> > which will tell you whether you are blocking or not. We are already
> > using a similar construct for arming a background timer in this case.
>
> Can we examine if vcpu->run->exit_reason == WFE/WFI and avoid setting
> preempted state if so?
We never go back to userspace for WFI/WFE, so no reason to populate
the run structure.
Checking for the blocked state is the right thing to do, and we
already have the primitive for this. Just use it.
M.
--
Without deviation from the norm, progress is not possible.
next prev parent reply other threads:[~2021-07-21 11:08 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-09 4:37 [PATCHv2 0/4] arm64:kvm: teach guest sched that VCPUs can be preempted Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-09 4:37 ` [PATCHv2 1/4] arm64: smccc: Add SMCCC pv-vcpu-state function call IDs Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-12 14:22 ` Marc Zyngier
2021-07-12 14:22 ` Marc Zyngier
2021-07-12 14:22 ` Marc Zyngier
2021-07-09 4:37 ` [PATCHv2 2/4] arm64: add guest pvstate support Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-09 7:39 ` David Edmondson
2021-07-09 7:39 ` David Edmondson
2021-07-09 7:39 ` David Edmondson
2021-07-09 7:52 ` Sergey Senozhatsky
2021-07-09 7:52 ` Sergey Senozhatsky
2021-07-09 7:52 ` Sergey Senozhatsky
2021-07-09 18:58 ` Joel Fernandes
2021-07-09 18:58 ` Joel Fernandes
2021-07-09 18:58 ` Joel Fernandes
2021-07-09 21:53 ` Sergey Senozhatsky
2021-07-09 21:53 ` Sergey Senozhatsky
2021-07-09 21:53 ` Sergey Senozhatsky
2021-07-11 16:58 ` Joel Fernandes
2021-07-11 16:58 ` Joel Fernandes
2021-07-11 16:58 ` Joel Fernandes
2021-07-12 15:42 ` Marc Zyngier
2021-07-12 15:42 ` Marc Zyngier
2021-07-12 15:42 ` Marc Zyngier
2021-07-21 2:05 ` Sergey Senozhatsky
2021-07-21 2:05 ` Sergey Senozhatsky
2021-07-21 2:05 ` Sergey Senozhatsky
2021-07-21 8:22 ` Marc Zyngier
2021-07-21 8:22 ` Marc Zyngier
2021-07-21 8:22 ` Marc Zyngier
2021-07-21 8:47 ` Sergey Senozhatsky
2021-07-21 8:47 ` Sergey Senozhatsky
2021-07-21 8:47 ` Sergey Senozhatsky
2021-07-21 10:16 ` Marc Zyngier
2021-07-21 10:16 ` Marc Zyngier
2021-07-21 10:16 ` Marc Zyngier
2021-07-09 4:37 ` [PATCHv2 3/4] arm64: do not use dummy vcpu_is_preempted() Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-12 15:47 ` Marc Zyngier
2021-07-12 15:47 ` Marc Zyngier
2021-07-12 15:47 ` Marc Zyngier
2021-07-21 2:06 ` Sergey Senozhatsky
2021-07-21 2:06 ` Sergey Senozhatsky
2021-07-21 2:06 ` Sergey Senozhatsky
2021-07-09 4:37 ` [PATCHv2 4/4] arm64: add host pv-vcpu-state support Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-09 4:37 ` Sergey Senozhatsky
2021-07-12 16:24 ` Marc Zyngier
2021-07-12 16:24 ` Marc Zyngier
2021-07-12 16:24 ` Marc Zyngier
2021-07-20 18:44 ` Joel Fernandes
2021-07-20 18:44 ` Joel Fernandes
2021-07-20 18:44 ` Joel Fernandes
2021-07-21 8:40 ` Marc Zyngier
2021-07-21 8:40 ` Marc Zyngier
2021-07-21 8:40 ` Marc Zyngier
2021-07-21 10:38 ` Sergey Senozhatsky
2021-07-21 10:38 ` Sergey Senozhatsky
2021-07-21 10:38 ` Sergey Senozhatsky
2021-07-21 11:08 ` Marc Zyngier [this message]
2021-07-21 11:08 ` Marc Zyngier
2021-07-21 11:08 ` Marc Zyngier
2021-07-21 1:15 ` Sergey Senozhatsky
2021-07-21 1:15 ` Sergey Senozhatsky
2021-07-21 1:15 ` Sergey Senozhatsky
2021-07-21 9:10 ` Marc Zyngier
2021-07-21 9:10 ` Marc Zyngier
2021-07-21 9:10 ` Marc Zyngier
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