linux-kernel - Re: [PATCH] kvm: fast-path msi injection with irqfd

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Message-ID: <20101119155427.GA20279@amt.cnet>
Date:	Fri, 19 Nov 2010 13:54:27 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Gleb Natapov <gleb@...hat.com>,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Gregory Haskins <ghaskins@...ell.com>,
	Chris Lalancette <clalance@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: fast-path msi injection with irqfd

On Thu, Nov 18, 2010 at 07:09:08PM +0200, Michael S. Tsirkin wrote:
> Store irq routing table pointer in the irqfd object,
> and use that to inject MSI directly without bouncing out to
> a kernel thread.
> 
> While we touch this structure, rearrange irqfd fields to make fastpath
> better packed for better cache utilization.
> 
> This also adds some comments about locking rules and rcu usage in code.
> 
> Some notes on the design:
> - Use pointer into the rt instead of copying an entry,
>   to make it possible to use rcu, thus side-stepping
>   locking complexities.  We also save some memory this way.
> - Old workqueue code is still used for level irqs.
>   I don't think we DTRT with level anyway, however,
>   it seems easier to keep the code around as
>   it has been thought through and debugged, and fix level later than
>   rip out and re-instate it later.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> 
> OK, this seems to work fine for me. Tested with virtio-net in guest
> with and without vhost-net.  Pls review/apply if appropriate.

Acked-by: Marcelo Tosatti <mtosatti@...hat.com>

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