From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jan Kiszka <jan.kiszka@web.de>
Cc: Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>, kvm <kvm@vger.kernel.org>,
Alex Williamson <alex.williamson@redhat.com>,
Jan Kiszka <jan.kiszka@siemens.com>
Subject: Re: [PATCH v3 5/5] KVM: Allow host IRQ sharing for passed-through PCI 2.3 devices
Date: Wed, 3 Nov 2010 11:10:45 +0200 [thread overview]
Message-ID: <20101103091045.GH6772@redhat.com> (raw)
In-Reply-To: <4CD123B8.8080607@web.de>
On Wed, Nov 03, 2010 at 09:56:24AM +0100, Jan Kiszka wrote:
> > Hmm, this does an extra config read on each interrupt (another one is in
> > pci_2_3_irq_unmask). These reads are pretty expensive... I do realize
> > locking becomes ugly, though. Maybe my idea to avoid set level to 0
> > was silly? Thoughts?
>
> Well, reading twice is the price to pay here, putting kvm_set_irq under
> spin_lock_irq again is a no-go. From that POV, the previous version was
> probably the cheapest: no extra efforts in the common case, but still
> avoiding reassertion via the host IRQ handler whenever possible.
>
> Jan
>
Sigh. I guess so. Any chance of a benchmark to let us figure this out?
--
MST
next parent reply other threads:[~2010-11-03 9:10 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1288771873.git.jan.kiszka@web.de>
[not found] ` <628f014fb1efb8e2208db03d13198ba301a3a34c.1288771873.git.jan.kiszka@web.de>
[not found] ` <20101103082921.GD6772@redhat.com>
[not found] ` <4CD123B8.8080607@web.de>
2010-11-03 9:10 ` Michael S. Tsirkin [this message]
2010-11-03 9:18 ` [PATCH v3 5/5] KVM: Allow host IRQ sharing for passed-through PCI 2.3 devices Jan Kiszka
[not found] ` <20101103084320.GF6772@redhat.com>
[not found] ` <4CD1227E.9020908@web.de>
2010-11-03 9:05 ` Michael S. Tsirkin
2010-11-03 9:15 ` Jan Kiszka
2010-11-03 9:18 ` Michael S. Tsirkin
2010-11-03 15:57 ` Alex Williamson
2010-11-03 17:27 ` Jan Kiszka
2010-11-03 17:35 ` Jan Kiszka
2010-11-03 17:42 ` Michael S. Tsirkin
2010-11-03 17:37 ` Michael S. Tsirkin
2010-11-03 17:45 ` Jan Kiszka
[not found] ` <128511f28870098dbd57bdaa081dd30ac2af70df.1288771873.git.jan.kiszka@web.de>
2010-11-03 22:13 ` [PATCH v3 2/5] KVM: Switch assigned device IRQ forwarding to threaded handler Marcelo Tosatti
2010-11-03 22:32 ` Jan Kiszka
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