From: Christoffer Dall <christoffer.dall@linaro.org>
To: Marc Zyngier <marc.zyngier@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 6/8] KVM: arm/arm64: timer: Add active state caching
Date: Wed, 10 Feb 2016 13:44:59 +0100 [thread overview]
Message-ID: <20160210124459.GM5171@cbox> (raw)
In-Reply-To: <1454931622-14902-7-git-send-email-marc.zyngier@arm.com>
On Mon, Feb 08, 2016 at 11:40:20AM +0000, Marc Zyngier wrote:
> Programming the active state in the (re)distributor can be an
> expensive operation so it makes some sense to try and reduce
> the number of accesses as much as possible. So far, we
> program the active state on each VM entry, but there is some
> opportunity to do less.
>
> An obvious solution is to cache the active state in memory,
> and only program it in the HW when conditions change. But
> because the HW can also change things under our feet (the active
> state can transition from 1 to 0 when the guest does an EOI),
> some precautions have to be taken, which amount to only caching
> an "inactive" state, and always programing it otherwise.
>
> With this in place, we observe a reduction of around 700 cycles
> on a 2GHz GICv2 platform for a NULL hypercall.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
WARNING: multiple messages have this Message-ID (diff)
From: christoffer.dall@linaro.org (Christoffer Dall)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 6/8] KVM: arm/arm64: timer: Add active state caching
Date: Wed, 10 Feb 2016 13:44:59 +0100 [thread overview]
Message-ID: <20160210124459.GM5171@cbox> (raw)
In-Reply-To: <1454931622-14902-7-git-send-email-marc.zyngier@arm.com>
On Mon, Feb 08, 2016 at 11:40:20AM +0000, Marc Zyngier wrote:
> Programming the active state in the (re)distributor can be an
> expensive operation so it makes some sense to try and reduce
> the number of accesses as much as possible. So far, we
> program the active state on each VM entry, but there is some
> opportunity to do less.
>
> An obvious solution is to cache the active state in memory,
> and only program it in the HW when conditions change. But
> because the HW can also change things under our feet (the active
> state can transition from 1 to 0 when the guest does an EOI),
> some precautions have to be taken, which amount to only caching
> an "inactive" state, and always programing it otherwise.
>
> With this in place, we observe a reduction of around 700 cycles
> on a 2GHz GICv2 platform for a NULL hypercall.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
next prev parent reply other threads:[~2016-02-10 12:44 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-08 11:40 [PATCH 0/8] KVM/ARM: Guest Entry/Exit optimizations Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-08 11:40 ` [PATCH 1/8] arm64: KVM: Switch the sys_reg search to be a binary search Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall
2016-02-10 12:44 ` Christoffer Dall
2016-02-10 13:49 ` Alex Bennée
2016-02-10 13:49 ` Alex Bennée
2016-02-10 14:00 ` Marc Zyngier
2016-02-10 14:00 ` Marc Zyngier
2016-02-08 11:40 ` [PATCH 2/8] ARM: KVM: Properly sort the invariant table Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall
2016-02-10 12:44 ` Christoffer Dall
2016-02-08 11:40 ` [PATCH 3/8] ARM: KVM: Enforce sorting of all CP tables Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall
2016-02-10 12:44 ` Christoffer Dall
2016-02-08 11:40 ` [PATCH 4/8] ARM: KVM: Rename struct coproc_reg::is_64 to is_64bit Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall
2016-02-10 12:44 ` Christoffer Dall
2016-02-08 11:40 ` [PATCH 5/8] ARM: KVM: Switch the CP reg search to be a binary search Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall
2016-02-10 12:44 ` Christoffer Dall
2016-02-08 11:40 ` [PATCH 6/8] KVM: arm/arm64: timer: Add active state caching Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall [this message]
2016-02-10 12:44 ` Christoffer Dall
2016-02-08 11:40 ` [PATCH 7/8] KVM: arm/arm64: Avoid accessing GICH registers Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-10 12:45 ` Christoffer Dall
2016-02-10 12:45 ` Christoffer Dall
2016-02-10 13:34 ` Marc Zyngier
2016-02-10 13:34 ` Marc Zyngier
2016-02-10 17:30 ` Christoffer Dall
2016-02-10 17:30 ` Christoffer Dall
2016-02-10 17:43 ` Marc Zyngier
2016-02-10 17:43 ` Marc Zyngier
2016-02-08 11:40 ` [PATCH 8/8] KVM: arm64: Avoid accessing ICH registers Marc Zyngier
2016-02-08 11:40 ` Marc Zyngier
2016-02-10 12:45 ` Christoffer Dall
2016-02-10 12:45 ` Christoffer Dall
2016-02-10 16:47 ` Marc Zyngier
2016-02-10 16:47 ` Marc Zyngier
2016-02-09 20:59 ` [PATCH 0/8] KVM/ARM: Guest Entry/Exit optimizations Christoffer Dall
2016-02-09 20:59 ` Christoffer Dall
2016-02-10 8:34 ` Marc Zyngier
2016-02-10 8:34 ` Marc Zyngier
2016-02-10 12:02 ` Andrew Jones
2016-02-10 12:02 ` Andrew Jones
2016-02-10 12:24 ` Marc Zyngier
2016-02-10 12:24 ` Marc Zyngier
2016-02-10 20:40 ` Christoffer Dall
2016-02-10 20:40 ` Christoffer Dall
2016-02-16 20:05 ` Marc Zyngier
2016-02-16 20:05 ` Marc Zyngier
2016-02-17 9:15 ` Christoffer Dall
2016-02-17 9:15 ` Christoffer Dall
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