Re: [PATCH v4] kvm: Use a bitmap for tracking used GSIs

From: Alex Williamson <alex.williamson@hp.com>
To: Avi Kivity <avi@redhat.com>
Cc: kvm@vger.kernel.org, sheng.yang@intel.com, mst@redhat.com
Subject: Re: [PATCH v4] kvm: Use a bitmap for tracking used GSIs
Date: Wed, 13 May 2009 07:11:16 -0600	[thread overview]
Message-ID: <1242220276.4786.67.camel@2710p.home> (raw)
In-Reply-To: <4A0AC453.2000907@redhat.com>

On Wed, 2009-05-13 at 16:00 +0300, Avi Kivity wrote:
> Alex Williamson wrote:
> >>
> >> When you say "multiple times", it is several, or a lot more?
> >>
> >> Maybe it is NAPI?
> >>     
> >
> > The system would run out of the ~1000 available GSIs in a minute or two
> > with just an e1000e available to the guest.  So that's something on the
> > order of 10/s.  This also causes a printk in the host ever time the
> > interrupt in enabled, which can't help performance and gets pretty
> > annoying for syslog.  I was guessing some kind of interrupt mitigation,
> > such as NAPI, but a qlogic FC card seems to do it too (seemingly at a
> > slower rate).
> >   
> 
> I see.  And what is the path by which it is disabled?  The mask bit in 
> the MSI entry?

Yes, I believe the only path is via a write to the MSI capability in the
PCI config space.

Alex