linux-kernel - Re: [RFC PATCH 00/17] virtual-bus

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Date:	Thu, 02 Apr 2009 11:09:35 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Avi Kivity <avi@...hat.com>
CC:	Gregory Haskins <ghaskins@...ell.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	agraf@...e.de, pmullaney@...ell.com, pmorreale@...ell.com,
	rusty@...tcorp.com.au, netdev@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [RFC PATCH 00/17] virtual-bus

Anthony Liguori wrote:
> Avi Kivity wrote:
>> Avi Kivity wrote:
>>>
>>> The alternative is to get a notification from the stack that the 
>>> packet is done processing.  Either an skb destructor in the kernel, 
>>> or my new API that everyone is not rushing out to implement.
>>
>> btw, my new api is
>>
>>
>>   io_submit(..., nr, ...): submit nr packets
>>   io_getevents(): complete nr packets
>
> I don't think we even need that to end this debate.  I'm convinced we 
> have a bug somewhere.  Even disabling TX mitigation, I see a ping 
> latency of around 300ns whereas it's only 50ns on the host.  This 
> defies logic so I'm now looking to isolate why that is.

I'm down to 90us.  Obviously, s/ns/us/g above.  The exec.c changes were 
the big winner... I hate qemu sometimes.

I'm pretty confident I can get at least to Greg's numbers with some 
poking.  I think I understand why he's doing better after reading his 
patches carefully but I also don't think it'll scale with many guests 
well...  stay tuned.

But most importantly, we are darn near where vbus is with this patch wrt 
added packet latency and this is totally from userspace with no host 
kernel changes.

So no, userspace is not the issue.

Regards,

Anthony Liguori

> Regards,
>
> Anthony Liguori
>

View attachment "first-pass.patch" of type "text/x-patch" (6597 bytes)