From: Christoffer Dall <christoffer.dall@linaro.org>
To: Marc Zyngier <marc.zyngier@arm.com>
Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 0/8] KVM/ARM: Guest Entry/Exit optimizations
Date: Wed, 17 Feb 2016 10:15:49 +0100 [thread overview]
Message-ID: <20160217091549.GB6696@cbox> (raw)
In-Reply-To: <56C38109.3020501@arm.com>
On Tue, Feb 16, 2016 at 08:05:29PM +0000, Marc Zyngier wrote:
> On 10/02/16 20:40, Christoffer Dall wrote:
> > On Mon, Feb 08, 2016 at 11:40:14AM +0000, Marc Zyngier wrote:
> >> I've recently been looking at our entry/exit costs, and profiling
> >> figures did show some very low hanging fruits.
> >>
> >> The most obvious cost is that accessing the GIC HW is slow. As in
> >> "deadly slow", specially when GICv2 is involved. So not hammering the
> >> HW when there is nothing to write is immediately beneficial, as this
> >> is the most common cases (whatever people seem to think, interrupts
> >> are a *rare* event).
> >>
> >> Another easy thing to fix is the way we handle trapped system
> >> registers. We do insist on (mostly) sorting them, but we do perform a
> >> linear search on trap. We can switch to a binary search for free, and
> >> get immediate benefits (the PMU code, being extremely trap-happy,
> >> benefits immediately from this).
> >>
> >> With these in place, I see an improvement of 20 to 30% (depending on
> >> the platform) on our world-switch cycle count when running a set of
> >> hand-crafted guests that are designed to only perform traps.
> >>
> >
> > By the way, I took this whole stack of changes (wsinc, vhe, and
> > optimizations) and ran it on Mustang and fired up UEFI and did a reboot
> > and things seem to work, so that's a small shallow
> > 'tested-by-something-else-than-a-linux-guest' statement from me.
>
> I've ran a slightly heavier set of tests, and the infamous reboot loop
> broke, thanks to patch #7.
>
> Notice how we fail to wipe the vgic_apr copy on the "light" exit path?
> If you're unlucky (and odds are that you will be), you will inject an
> interrupt while its active priority bit is set, and the new interrupt
> won't be delivered. Bah.
>
> With that fixed, the reboot loop has been going strong for a few hours.
> I'll leave my Seattle cooking overnight and if everything looks good in
> the morning, I'll repost a new set of patches.
>
Good that you caught this one then!
-Christoffer
prev parent reply other threads:[~2016-02-17 9:15 UTC|newest]
Thread overview: 30+ 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 ` [PATCH 1/8] arm64: KVM: Switch the sys_reg search to be a binary search Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall
2016-02-10 13:49 ` Alex Bennée
2016-02-10 14:00 ` Marc Zyngier
2016-02-08 11:40 ` [PATCH 2/8] ARM: KVM: Properly sort the invariant table Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall
2016-02-08 11:40 ` [PATCH 3/8] ARM: KVM: Enforce sorting of all CP tables Marc Zyngier
2016-02-10 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
2016-02-10 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
2016-02-10 12:44 ` Christoffer Dall
2016-02-08 11:40 ` [PATCH 6/8] KVM: arm/arm64: timer: Add active state caching Marc Zyngier
2016-02-10 12:44 ` Christoffer Dall
2016-02-08 11:40 ` [PATCH 7/8] KVM: arm/arm64: Avoid accessing GICH registers Marc Zyngier
2016-02-10 12:45 ` Christoffer Dall
2016-02-10 13:34 ` Marc Zyngier
2016-02-10 17:30 ` Christoffer Dall
2016-02-10 17:43 ` Marc Zyngier
2016-02-08 11:40 ` [PATCH 8/8] KVM: arm64: Avoid accessing ICH registers Marc Zyngier
2016-02-10 12:45 ` Christoffer Dall
2016-02-10 16:47 ` Marc Zyngier
2016-02-09 20:59 ` [PATCH 0/8] KVM/ARM: Guest Entry/Exit optimizations Christoffer Dall
2016-02-10 8:34 ` Marc Zyngier
2016-02-10 12:02 ` Andrew Jones
2016-02-10 12:24 ` Marc Zyngier
2016-02-10 20:40 ` Christoffer Dall
2016-02-16 20:05 ` Marc Zyngier
2016-02-17 9:15 ` Christoffer Dall [this message]
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