From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH] KVM: x86: inline kvm_ioapic_handles_vector()
Date: Mon, 23 Mar 2015 21:17:44 -0300
Message-ID: <20150324001743.GA16287@amt.cnet>
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Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>
To: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
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On Thu, Mar 19, 2015 at 09:52:41PM +0100, Radim Kr=C4=8Dm=C3=A1=C5=99 w=
rote:
> An overhead from function call is not appropriate for its size and
> frequency of execution.
>=20
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Radim Kr=C4=8Dm=C3=A1=C5=99 <rkrcmar@redhat.com>
> ---
>   I'm not very fond of that smp_rmb(): there is no real synchronizati=
on
>   against update_handled_vectors(),=20

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=
=2E

test_bit has volatile on *addr, so don't see why the smp_rmb is
necessary at all.

Applied, thanks.