linux-kernel - Re: [PATCH] arm64: KVM: Save two instructions in __guest

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Message-ID: <20160825133122.GA8016@lvm>
Date:   Thu, 25 Aug 2016 15:31:22 +0200
From:   Christoffer Dall <christoffer.dall@...aro.org>
To:     Shanker Donthineni <shankerd@...eaurora.org>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>
Subject: Re: [PATCH] arm64: KVM: Save two instructions in __guest_enter()

Hi Shanker,

On Tue, Aug 09, 2016 at 08:15:36PM -0500, Shanker Donthineni wrote:
> We are doing an unnecessary stack push/pop operation when restoring
> the guest registers x0-x18 in __guest_enter(). This patch saves the
> two instructions by using x18 as a base register. No need to store
> the vcpu context pointer in stack because it is redundant and not
> being used anywhere, the same information is available in tpidr_el2.

Does this have any measureable benefit?

Thanks,
-Christoffer