From: Gleb Natapov <gleb@redhat.com>
To: Jan Kiszka <jan.kiszka@web.de>
Cc: Avi Kivity <avi@redhat.com>, kvm-devel <kvm@vger.kernel.org>
Subject: Re: assign-dev: Purpose of interrupt_work
Date: Mon, 12 Oct 2009 09:45:13 +0200 [thread overview]
Message-ID: <20091012074513.GV16702@redhat.com> (raw)
In-Reply-To: <4AD2DA57.6030006@web.de>
On Mon, Oct 12, 2009 at 09:27:19AM +0200, Jan Kiszka wrote:
> Gleb Natapov wrote:
> > On Mon, Oct 12, 2009 at 09:03:18AM +0200, Jan Kiszka wrote:
> >> Hi,
> >>
> >> I was starring at the IRQ delivery path of assigned devices for a while,
> >> wondering why we have a work queue there. Now, after looking at some
> >> prehistoric versions, I think the reason is that there once was a mutex
> >> involved while we now use RCU. Am I right that we could actually drop
> >> this indirection today?
> >>
> > ioapic/pic path still has mutex. If MSIX is used (like it should) we can
> > drop work queue.
>
> I see. Wouldn't it be feasible to convert the fast paths of [io]apic to
> spinlocks?
>
Apic is lockless. For ioapic/pic I used spinlocks initially, but Avi
prefers mutexes. Theoretically it is possible to make them lockless,
but code will be complex and eventually more slow, since more then two
atomic operation will be used on irq injection path.
--
Gleb.
next prev parent reply other threads:[~2009-10-12 7:45 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-12 7:03 assign-dev: Purpose of interrupt_work Jan Kiszka
2009-10-12 7:13 ` Gleb Natapov
2009-10-12 7:27 ` Jan Kiszka
2009-10-12 7:45 ` Gleb Natapov [this message]
2009-10-12 7:50 ` Jan Kiszka
2009-10-12 7:57 ` Gleb Natapov
2009-10-12 8:16 ` Jan Kiszka
2009-10-12 8:39 ` Gleb Natapov
2009-10-12 9:04 ` Jan Kiszka
2009-10-12 9:14 ` Avi Kivity
2009-10-12 9:25 ` Jan Kiszka
2009-10-12 9:30 ` Avi Kivity
2009-10-12 9:38 ` Gleb Natapov
2009-10-12 9:40 ` Avi Kivity
2009-10-12 9:42 ` Gleb Natapov
2009-10-12 9:14 ` Gleb Natapov
2009-10-12 8:39 ` Avi Kivity
2009-10-12 9:05 ` Gleb Natapov
2009-10-12 9:07 ` Avi Kivity
2009-10-12 9:07 ` Jan Kiszka
2009-10-12 9:16 ` Avi Kivity
2009-10-12 17:36 ` Marcelo Tosatti
2009-10-12 20:44 ` Jan Kiszka
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