From: Gleb Natapov <gleb@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Chris Lalancette <clalance@redhat.com>,
kvm@vger.kernel.org, Marcelo Tosatti <mtosatti@redhat.com>,
Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH v3 1/3] Introduce a workqueue to deliver PIT timer interrupts.
Date: Tue, 17 Apr 2012 12:31:23 +0300 [thread overview]
Message-ID: <20120417093123.GB11918@redhat.com> (raw)
In-Reply-To: <4F8C49D6.9010603@siemens.com>
On Mon, Apr 16, 2012 at 06:33:26PM +0200, Jan Kiszka wrote:
> On 2010-06-16 23:11, Chris Lalancette wrote:
> > We really want to "kvm_set_irq" during the hrtimer callback,
> > but that is risky because that is during interrupt context.
> > Instead, offload the work to a workqueue, which is a bit safer
> > and should provide most of the same functionality.
>
> Unfortunately, workqueues do not have fixed kthread associations (and
> "kvm-pit-wq" would be too unspecific when running multiple VMs). So I
> just realized that this subtly breaks the ability to run KVM guests with
> RT priority (boot managers with timeouts hang as the workqueue starves).
>
> Before throwing some kthread_worker at this, could someone help me
> recalling what was "risky" here? That the PIT IRQ may have to be
> broadcast to a large number of VCPUs? I would offer to include this
> information in my changelog. ;)
>
ioapic and pic irq_set functions uses spinlocks, but not irqsave
variants. Also I am always forget whether is is safe to kick vcpu from
irq context.
--
Gleb.
next prev parent reply other threads:[~2012-04-17 9:31 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-16 21:11 [PATCH v3 0/3]: Fixes to IRQ routing Chris Lalancette
2010-06-16 21:11 ` [PATCH v3 1/3] Introduce a workqueue to deliver PIT timer interrupts Chris Lalancette
2012-04-16 16:33 ` Jan Kiszka
2012-04-16 17:07 ` Avi Kivity
2012-04-17 9:31 ` Gleb Natapov [this message]
2012-04-17 10:23 ` Avi Kivity
2012-04-17 10:26 ` Gleb Natapov
2012-04-17 10:29 ` Avi Kivity
2012-04-17 10:31 ` Gleb Natapov
2012-04-17 10:42 ` Avi Kivity
2012-04-17 10:43 ` Avi Kivity
2012-04-17 11:05 ` Gleb Natapov
2012-04-17 12:00 ` Avi Kivity
2012-04-17 12:03 ` Gleb Natapov
2012-04-17 12:06 ` Avi Kivity
2012-04-17 16:15 ` Jan Kiszka
2012-04-17 16:17 ` Avi Kivity
2012-04-18 8:04 ` Gleb Natapov
2012-04-18 8:25 ` Avi Kivity
2012-04-18 8:27 ` Gleb Natapov
2010-06-16 21:11 ` [PATCH v3 2/3] Allow any LAPIC to accept PIC interrupts Chris Lalancette
2010-06-16 21:11 ` [PATCH v3 3/3] In DM_LOWEST, only deliver interrupts to vcpus with enabled LAPIC's Chris Lalancette
2010-06-18 17:44 ` [PATCH v3 0/3]: Fixes to IRQ routing Marcelo Tosatti
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