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

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Message-ID: <4B312252.4040009@gmail.com>
Date:	Tue, 22 Dec 2009 14:47:30 -0500
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>, 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 12/22/09 2:43 PM, Avi Kivity wrote:
> On 12/22/2009 09:41 PM, Gregory Haskins wrote:
>>
>>> It means that kvm locking suddenly affects more of the kernel.
>>>
>>>      
>> Thats ok.  This would only be w.r.t. devices that are bound to the KVM
>> instance anyway, so they better know what they are doing (and they do).
>>
>>    
> 
> It's okay to the author of that device.  It's not okay to the kvm
> developers who are still evolving the locking and have to handle all
> devices that use xinterface.

Perhaps, but like it or not, if you want to do in-kernel you need to
invoke backends.  And if you want to invoke backends, limiting it to
thread wakeups is, well, limiting.  For one, you miss out on that
exploit I mentioned earlier which can help sometimes.

Besides, the direction that Marcelo and I left the mmio/pio bus was that
it would go lockless eventually, not "more lockful" ;)

Has that changed?  I honestly haven't followed whats going on in the
io-bus code in a while.

-Greg



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