linux-kernel - Re: [RFC PATCH] KVM: arm/arm64: Enable direct irqfd MSI injection

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Message-ID: <20190318133040.1cfad9a4@why.wild-wind.fr.eu.org>
Date:   Mon, 18 Mar 2019 13:30:40 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Zenghui Yu <yuzenghui@...wei.com>
Cc:     <christoffer.dall@....com>, <eric.auger@...hat.com>,
        <andre.przywara@....com>, <james.morse@....com>,
        <julien.thierry@....com>, <suzuki.poulose@....com>,
        <kvmarm@...ts.cs.columbia.edu>, <mst@...hat.com>,
        <pbonzini@...hat.com>, <rkrcmar@...hat.com>, <kvm@...r.kernel.org>,
        <wanghaibin.wang@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        "Raslan, KarimAllah" <karahmed@...zon.de>
Subject: Re: [RFC PATCH] KVM: arm/arm64: Enable direct irqfd MSI injection

On Sun, 17 Mar 2019 19:35:48 +0000
Marc Zyngier <marc.zyngier@....com> wrote:

[...]

> A first approach would be to keep a small cache of the last few
> successful translations for this ITS, cache that could be looked-up by
> holding a spinlock instead. A hit in this cache could directly be
> injected. Any command that invalidates or changes anything (DISCARD,
> INV, INVALL, MAPC with V=0, MAPD with V=0, MOVALL, MOVI) should nuke
> the cache altogether.

And to explain what I meant with this, I've pushed a branch[1] with a
basic prototype. It is good enough to get a VM to boot, but I wouldn't
trust it for anything serious just yet.

If anyone feels like giving it a go and check whether it has any
benefit performance wise, please do so.

Thanks,

	M.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/its-translation-cache
-- 
Without deviation from the norm, progress is not possible.