From: Marcelo Tosatti <mtosatti@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] KVM: x86: inline kvm_ioapic_handles_vector()
Date: Mon, 23 Mar 2015 21:17:44 -0300 [thread overview]
Message-ID: <20150324001743.GA16287@amt.cnet> (raw)
In-Reply-To: <1426798361-14982-1-git-send-email-rkrcmar@redhat.com>
On Thu, Mar 19, 2015 at 09:52:41PM +0100, Radim Krčmář wrote:
> An overhead from function call is not appropriate for its size and
> frequency of execution.
>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
> I'm not very fond of that smp_rmb(): there is no real synchronization
> against update_handled_vectors(),
Yes, because the guest OS should provide synchronization (it should
shutdown interrupts before attempting to modify IOAPIC table).
The smp_wmb is necessary.
> so the only point I see is to drop
> cached value of handled_vectors, which seems like bad use of LFENCE.
test_bit has volatile on *addr, so don't see why the smp_rmb is
necessary at all.
Applied, thanks.
prev parent reply other threads:[~2015-03-24 0:20 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-19 20:52 [PATCH] KVM: x86: inline kvm_ioapic_handles_vector() Radim Krčmář
2015-03-24 0:17 ` Marcelo Tosatti [this message]
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