From: Paolo Bonzini <pbonzini@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>, Peter Xu <peterx@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
x86@kernel.org, "Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH] KVM: lapic: stop advertising DIRECTED_EOI when in-kernel IOAPIC is in use
Date: Mon, 12 Feb 2018 12:31:27 +0100 [thread overview]
Message-ID: <4d3e535c-3f26-0a7e-efd7-fd55fd4928e8@redhat.com> (raw)
In-Reply-To: <87r2pqxx6r.fsf@vitty.brq.redhat.com>
On 12/02/2018 12:30, Vitaly Kuznetsov wrote:
>> - Radim's suggestion was to disable DIRECTED_EOI unconditionally but I'm not
>> that radical :-) In theory, we may have multiple IOAPICs in userspace in
>> future and DIRECTED_EOI can be leveraged.
>
> I sort of agree on this, especially considering that we already have
> IOAPIC version 0x20 support in QEMU already.
Yeah, and directed EOI is faster AFAIU.
> My thoughts were: with in-kernel IOAPIC nobody does EOI broadcast
> disabling today or he's already broken -- there's no way to EOI
> level-triggered interrupts. And the patch changes nothing for QEMU
> ioapic implementation.
>
> What I'm not sure about is if we allow migration between in-kernel and
> QEMU ioapic implementations. I don't think so but in case we do it is
> again already broken because going down from 0x20 to 0x11 will leave you
> without EOI register. Migrating from 0x11 to 0x20 should be fine, the
> guest will continue without knowing there's a new feature available.
No, we don't allow that.
Paolo
next prev parent reply other threads:[~2018-02-12 11:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-09 13:01 [PATCH] KVM: lapic: stop advertising DIRECTED_EOI when in-kernel IOAPIC is in use Vitaly Kuznetsov
2018-02-09 15:20 ` Nikita Leshenko
2018-02-09 16:32 ` Vitaly Kuznetsov
2018-02-11 5:25 ` Peter Xu
2018-02-12 11:30 ` Vitaly Kuznetsov
2018-02-12 11:31 ` Paolo Bonzini [this message]
2018-03-05 10:29 ` Vitaly Kuznetsov
2018-03-07 13:53 ` Radim Krčmář
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