From: Paolo Bonzini <pbonzini@redhat.com>
To: Jan Kiszka <jan.kiszka@web.de>
Cc: Gleb Natapov <gleb@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>, kvm <kvm@vger.kernel.org>
Subject: Re: [PATCH] KVM: x86: Convert INIT and SIPI signals into synchronously handled events
Date: Wed, 13 Mar 2013 10:03:07 +0100 [thread overview]
Message-ID: <514040CB.3070704@redhat.com> (raw)
In-Reply-To: <51402D1F.8000109@web.de>
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Il 13/03/2013 08:39, Jan Kiszka ha scritto:
>> I think this should clear pending SIPIs, unless KVM_APIC_INIT
>> was already set in which case it should be a no-op. Something
>> like:
>>
>> e = apic->pending_events; while (!(e & KVM_APIC_INIT)) e =
>> cmpxchg(&apic->pending_events, e, (e | KVM_APIC_INIT) &
>> ~KVM_APIC_SIPI);
>>
>> If you do this, better make pending_events an atomic_t.
>
> Quick question: Why atomic_t? It becomes a bit ugly to poke into
> the atomic counter for bitops, and cmpxchg is mapped on an
> interlocked version.
It's a bit safer because it forces you to use atomic_read, and
generally points out to reviewers to think about memory barriers. But
indeed the lack of atomic_set_bit and atomic_clear_bit makes the code
uglier. And as long as there are no other bits in
apic->pending_events, the above loop is actually the same as just
apic->pending_events = 1 << KVM_APIC_INIT;
Paolo
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next prev parent reply other threads:[~2013-03-13 9:03 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-12 11:44 [PATCH] KVM: x86: Convert INIT and SIPI signals into synchronously handled events Jan Kiszka
2013-03-12 12:06 ` Paolo Bonzini
2013-03-12 12:29 ` Gleb Natapov
2013-03-12 12:29 ` Paolo Bonzini
2013-03-12 12:46 ` Jan Kiszka
2013-03-12 12:49 ` Gleb Natapov
2013-03-12 12:52 ` Jan Kiszka
2013-03-12 12:53 ` Gleb Natapov
2013-03-12 13:09 ` Paolo Bonzini
2013-03-12 13:13 ` Jan Kiszka
2013-03-12 12:58 ` Jan Kiszka
2013-03-12 13:01 ` Jan Kiszka
2013-03-12 13:13 ` Paolo Bonzini
2013-03-12 13:16 ` Jan Kiszka
2013-03-12 13:25 ` Gleb Natapov
2013-03-12 13:27 ` Jan Kiszka
2013-03-12 13:37 ` Gleb Natapov
2013-03-13 7:39 ` Jan Kiszka
2013-03-13 9:03 ` Paolo Bonzini [this message]
2013-03-13 9:08 ` Jan Kiszka
2013-03-12 13:12 ` Gleb Natapov
2013-03-12 13:21 ` Jan Kiszka
2013-03-12 13:41 ` Gleb Natapov
2013-03-12 13:43 ` Paolo Bonzini
2013-03-12 13:52 ` Gleb Natapov
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