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

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Date:	Tue, 22 Dec 2009 14:37:28 -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 2:32 PM, Gregory Haskins wrote:
> On 12/22/09 2:25 PM, Avi Kivity wrote:

>>
>> If you're not doing something pretty minor, you're better of waking up a
>> thread (perhaps _sync if you want to keep on the same cpu).  With the
>> new user return notifier thingie, that's pretty cheap.
> 
> We have exploits that take advantage of IO heuristics.  When triggered
> they do more work in vcpu context than normal, which reduces latency
> under certain circumstances.  But you definitely do _not_ want to do
> them in-atomic ;)

And I almost forgot:  dev->call() is an RPC to the backend device.
Therefore, it must be synchronous, yet we dont want it locked either.  I
think that was actually the primary motivation for the change, now that
I think about it.

-Greg


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