linux-kernel - Re: [PATCH v5] enable x2APIC without interrupt remapping under KVM

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Date:	Sat, 04 Jul 2009 17:22:01 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Sheng Yang <sheng@...ux.intel.com>,
	"kvm\@vger.kernel.org" <kvm@...r.kernel.org>,
	"avi\@redhat.com" <avi@...hat.com>
Subject: Re: [PATCH v5] enable x2APIC without interrupt remapping under KVM

Gleb Natapov <gleb@...hat.com> writes:

>> Therefore I don't see the point of supporting one without the other.
> x2apic provide us with other benefits as commit message explains, and
> doesn't add any problems that we don't have now already.

If this code has a legitimate place on real hardware I am all for it.

If this is just a hack to make virtualization faster I don't like the
extra code paths in the middle core architecture code.  That will
be a support burden for the foreseeable future.  More code to
test etc. 

Quickly skimming the patch it just appears to stir a mess.
Plus it adds weird paravirtualization checks, ???

If we are going to have a special code path for virtual hardware
can we do it right and have something nice to use that makes life
simpler?  For what we want to do with ioapics they suck and are
really not suitable.  The only thing that recommends them is that
they are standard.  But you are deviating from the standard so
what is the point.

Eric

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