From: Sean Christopherson <seanjc@google.com>
To: Jon Kohler <jon@nutanix.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: x86: optimize PKU branching in kvm_load_{guest|host}_xsave_state
Date: Mon, 28 Mar 2022 14:51:21 +0000 [thread overview]
Message-ID: <YkHLaS2IPZDCToXk@google.com> (raw)
In-Reply-To: <1E31F2B6-96BF-42E0-AD41-3C512D98D74B@nutanix.com>
On Mon, Mar 28, 2022, Jon Kohler wrote:
>
>
> > On Mar 27, 2022, at 6:43 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> >
> > On 3/26/22 02:37, Jon Kohler wrote:
> >>>> Flip the ordering of the || condition so that XFEATURE_MASK_PKRU is
> >>>> checked first, which when instrumented in our environment appeared
> >>>> to be always true and less overall work than kvm_read_cr4_bits.
> >>>
> >>> If it's always true, then it should be checked last, not first. And if
> >> Sean thanks for the review. This would be a left handed || short circuit, so
> >> wouldn’t we want always true to be first?
> >
> > Yes.
>
> Ack, thanks.
Yeah, I lost track of whether it was a || or &&.
prev parent reply other threads:[~2022-03-28 14:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-24 0:44 [PATCH] KVM: x86: optimize PKU branching in kvm_load_{guest|host}_xsave_state Jon Kohler
2022-03-25 11:01 ` Paolo Bonzini
2022-03-26 0:15 ` Sean Christopherson
2022-03-26 1:37 ` Jon Kohler
2022-03-27 10:43 ` Paolo Bonzini
2022-03-28 0:53 ` Jon Kohler
2022-03-28 14:51 ` Sean Christopherson [this message]
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