From: Davide Libenzi <davidel@xmailserver.org>
To: Gregory Haskins <ghaskins@novell.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
kvm@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
avi@redhat.com, paulmck@linux.vnet.ibm.com,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier interface
Date: Wed, 17 Jun 2009 10:44:34 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.1.10.0906171034030.7891@makko.or.mcafeemobile.com> (raw)
In-Reply-To: <4A3927C0.5060607@novell.com>
On Wed, 17 Jun 2009, Gregory Haskins wrote:
> Can you elaborate? I currently do not see how I could do the proposed
> concept inside of irqfd while still using eventfd. Of course, that
> would be possible if we fork irqfd from eventfd, and perhaps this is
> what you are proposing. As previously stated I don't want to give up on
> the prospect of re-using it quite yet, so bear with me. :)
>
> The issue with eventfd, as I see it, is that eventfd uses a
> spin_lock_irqsave (by virtue of the wait-queue stuff) across the
> "signal" callback (which today is implemented as a wake-up). This
> spin_lock implicitly creates a non-preemptible critical section that
> occurs independently of whether eventfd_signal() itself is invoked from
> a sleepable context or not.
>
> What I strive to achieve is to remove the creation of this internal
> critical section. If eventfd_signal() is called from atomic context, so
> be it. We will detect this in the callback and be forced to take the
> slow-path, and I am ok with that. *But*, if eventfd_signal() (or
> f_ops->write(), for that matter) are called from a sleepable context
> *and* eventfd doesn't introduce its own critical section (such as with
> my srcu patch), we can potentially optimize within the callback by
> executing serially instead of deferring (e.g. via a workqueue).
Since when the scheduling (assuming it's not permanently running on
another core due to high frequency work post) of a kernel thread is such
a big impact that interfaces need to be redesigned for that?
How much the (possible, but not certain) kernel thread context switch time
weighs in the overall KVM IRQ service time?
> It can! :) This is not changing from whats in mainline today (covered
> above).
It can/could, if the signal() function takes very accurate care of doing
the magic atomic check.
- Davide
next prev parent reply other threads:[~2009-06-17 17:50 UTC|newest]
Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-16 2:29 [KVM-RFC PATCH 0/2] eventfd enhancements for irqfd/iosignalfd Gregory Haskins
2009-06-16 2:29 ` [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier interface Gregory Haskins
2009-06-16 14:02 ` Michael S. Tsirkin
2009-06-16 14:11 ` Gregory Haskins
2009-06-16 14:38 ` Michael S. Tsirkin
2009-06-16 14:48 ` Gregory Haskins
2009-06-16 14:54 ` Gregory Haskins
2009-06-16 15:16 ` Michael S. Tsirkin
2009-06-16 14:55 ` Michael S. Tsirkin
2009-06-16 15:20 ` Gregory Haskins
2009-06-16 15:41 ` Michael S. Tsirkin
2009-06-16 16:17 ` Gregory Haskins
2009-06-16 16:19 ` Davide Libenzi
2009-06-16 17:01 ` Gregory Haskins
2009-06-17 16:38 ` Davide Libenzi
2009-06-17 17:28 ` Gregory Haskins
2009-06-17 17:44 ` Davide Libenzi [this message]
2009-06-17 19:17 ` Gregory Haskins
2009-06-17 19:50 ` Davide Libenzi
2009-06-17 21:48 ` Gregory Haskins
2009-06-17 23:21 ` Davide Libenzi
2009-06-18 6:23 ` Michael S. Tsirkin
2009-06-18 17:52 ` Davide Libenzi
2009-06-18 14:01 ` Gregory Haskins
2009-06-18 14:01 ` Gregory Haskins
2009-06-18 17:44 ` Davide Libenzi
2009-06-18 19:04 ` Gregory Haskins
2009-06-18 19:04 ` Gregory Haskins
2009-06-18 22:03 ` Davide Libenzi
2009-06-18 22:47 ` Gregory Haskins
2009-06-18 22:47 ` Gregory Haskins
2009-06-19 18:51 ` Gregory Haskins
2009-06-19 18:51 ` [PATCH 1/3] eventfd: Allow waiters to be notified about the eventfd file* going away Gregory Haskins
2009-06-19 18:51 ` [PATCH 2/3] eventfd: add generalized notifier interface Gregory Haskins
2009-06-19 18:51 ` [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions Gregory Haskins
2009-06-19 19:10 ` Davide Libenzi
2009-06-19 21:16 ` Gregory Haskins
2009-06-19 21:26 ` Davide Libenzi
2009-06-19 21:49 ` Gregory Haskins
2009-06-19 21:54 ` Davide Libenzi
2009-06-19 22:47 ` Davide Libenzi
2009-06-20 2:09 ` Gregory Haskins
2009-06-20 21:17 ` Davide Libenzi
2009-06-20 22:11 ` Davide Libenzi
2009-06-20 23:48 ` Davide Libenzi
2009-06-21 1:14 ` Gregory Haskins
2009-06-21 16:51 ` Davide Libenzi
2009-06-21 18:39 ` Gregory Haskins
2009-06-21 23:54 ` Davide Libenzi
2009-06-22 16:05 ` Gregory Haskins
2009-06-22 16:05 ` Gregory Haskins
2009-06-22 17:01 ` Davide Libenzi
2009-06-22 17:43 ` Gregory Haskins
2009-06-22 17:43 ` Gregory Haskins
2009-06-22 18:03 ` Davide Libenzi
2009-06-22 18:31 ` Gregory Haskins
2009-06-22 18:31 ` Gregory Haskins
2009-06-22 18:40 ` Davide Libenzi
2009-06-22 18:41 ` Michael S. Tsirkin
2009-06-22 18:51 ` Davide Libenzi
2009-06-22 19:05 ` Michael S. Tsirkin
2009-06-22 19:26 ` Gregory Haskins
2009-06-22 19:29 ` Davide Libenzi
2009-06-22 20:06 ` Gregory Haskins
2009-06-22 22:53 ` Davide Libenzi
2009-06-23 1:03 ` Gregory Haskins
2009-06-23 1:17 ` Davide Libenzi
2009-06-23 1:26 ` Gregory Haskins
2009-06-23 1:26 ` Gregory Haskins
2009-06-23 14:29 ` Davide Libenzi
2009-06-23 14:37 ` Gregory Haskins
2009-06-23 14:37 ` Gregory Haskins
2009-06-23 14:35 ` Davide Libenzi
2009-06-23 14:42 ` Gregory Haskins
2009-06-23 14:42 ` Gregory Haskins
2009-06-23 15:04 ` Michael S. Tsirkin
2009-06-22 20:28 ` Michael S. Tsirkin
2009-06-22 19:16 ` Gregory Haskins
2009-06-22 19:54 ` Davide Libenzi
2009-06-24 3:25 ` Rusty Russell
2009-06-24 22:45 ` Davide Libenzi
2009-06-25 11:42 ` Rusty Russell
2009-06-25 16:34 ` Davide Libenzi
2009-06-25 17:32 ` Gregory Haskins
2009-06-25 18:26 ` Michael S. Tsirkin
2009-06-25 18:41 ` Gregory Haskins
2009-06-26 11:23 ` Michael S. Tsirkin
2009-06-23 3:25 ` Rusty Russell
2009-06-23 14:31 ` Davide Libenzi
2009-06-25 0:19 ` Davide Libenzi
2009-06-21 1:05 ` Gregory Haskins
2009-06-16 17:54 ` [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier interface Michael S. Tsirkin
2009-06-16 18:09 ` Gregory Haskins
2009-06-17 14:45 ` Michael S. Tsirkin
2009-06-17 15:02 ` Gregory Haskins
2009-06-17 16:25 ` Michael S. Tsirkin
2009-06-17 16:41 ` Gregory Haskins
2009-06-16 14:17 ` Gregory Haskins
2009-06-16 14:22 ` Gregory Haskins
2009-06-16 14:40 ` Gregory Haskins
2009-06-16 14:46 ` Michael S. Tsirkin
2009-06-18 9:03 ` Avi Kivity
2009-06-18 11:43 ` Gregory Haskins
2009-06-16 2:30 ` [KVM-RFC PATCH 2/2] eventfd: add module reference counting support for registered notifiers Gregory Haskins
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