linux-kernel - Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

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Date:	Thu, 24 Dec 2009 04:31:13 -0500
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Andi Kleen <andi@...stfloor.org>, kvm@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org,
	"alacrityvm-devel@...ts.sourceforge.net" 
	<alacrityvm-devel@...ts.sourceforge.net>
Subject: Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

On 12/23/09 3:36 PM, Avi Kivity wrote:
> On 12/23/2009 06:44 PM, Gregory Haskins wrote:
>>
>>>   - Are a pure software concept
>>>      
>> By design.  In fact, I would describe it as "software to software
>> optimized" as opposed to trying to shoehorn into something that was
>> designed as a software-to-hardware interface (and therefore has
>> assumptions about the constraints in that environment that are not
>> applicable in software-only).
>>
>>    
> 
> And that's the biggest mistake you can make.

Sorry, that is just wrong or you wouldn't have virtio either.

>  Look at Xen, for
> instance.  The paravirtualized the fork out of everything that moved in
> order to get x86 virt going.  And where are they now? x86_64 syscalls
> are slow since they have to trap to the hypervisor and (partially) flush
> the tlb.  With npt or ept capable hosts performance is better for many
> workloads on fullvirt.  And paravirt doesn't support Windows.  Their
> unsung hero Jeremy is still trying to upstream dom0 Xen support.  And
> they get to support it forever.

We are only talking about PV-IO here, so not apples to apples to what
Xen is going through.

> 
> VMware stuck with the hardware defined interfaces.  Sure they had to
> implement binary translation to get there, but as a result, they only
> have to support one interface, all guests support it, and they can drop
> it on newer hosts where it doesn't give them anything.

Again, you are confusing PV-IO.  Not relevant here.   Afaict, vmware,
kvm, xen, etc, all still do PV-IO and likely will for the foreseeable
future.

-Greg


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