From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>,
kvm@vger.kernel.org, "Wanpeng Li" <kernellwp@gmail.com>
Subject: Re: [PATCH] KVM: lapic: Reuse auto-adjusted timer advance of first stable vCPU
Date: Fri, 24 May 2019 13:23:33 -0700 [thread overview]
Message-ID: <20190524202333.GG365@linux.intel.com> (raw)
In-Reply-To: <3ea5ae51-89b2-ee0c-d156-88198af90b95@redhat.com>
On Mon, May 20, 2019 at 03:03:10PM +0200, Paolo Bonzini wrote:
> On 08/05/19 23:47, Sean Christopherson wrote:
> > +
> > + /*
> > + * The first vCPU to get a stable advancement time "wins" and
> > + * sets the advancement time that is used for *new* vCPUS that
> > + * are created with auto-adjusting enabled.
> > + */
> > + if (apic->lapic_timer.timer_advance_adjust_done)
> > + (void)cmpxchg(&adjusted_timer_advance_ns, -1,
> > + timer_advance_ns);
>
> This is relatively expensive, so it should only be done after setting
> timer_advance_adjust_done to true.
That's already the case, or am I missing something?
This code is inside "if (!apic->lapic_timer.timer_advance_adjust_done)",
and apic->lapic_timer.timer_advance_adjust_done is set to true at creation
time if "adjusted_timer_advance_ns != -1", i.e. the cmpxchg() will only
be reached on vCPUs that are created before adjusted_timer_advance_ns is
set and will be reached at most once per vCPU.
next prev parent reply other threads:[~2019-05-24 20:23 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-08 21:47 [PATCH] KVM: lapic: Reuse auto-adjusted timer advance of first stable vCPU Sean Christopherson
2019-05-20 13:03 ` Paolo Bonzini
2019-05-24 20:23 ` Sean Christopherson [this message]
2019-05-24 20:48 ` Paolo Bonzini
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