lkml.org 
[lkml]   [2009]   [Apr]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 00/17] virtual-bus
Gregory Haskins wrote:



>> There is no choice. Exiting from the guest to the kernel to userspace
>> is prohibitively expensive, you can't do that on every packet.
>>
>>
>
> Now you are making my point ;) This is part of the cost of your
> signaling path, and it directly adds to your latency time.

It adds a microsecond. The kvm overhead of putting things in userspace
is low enough, I don't know why people keep mentioning it. The problem
is the kernel/user networking interfaces.

> You can't
> buffer packets here if the guest is only going to send one and wait for
> a response and expect that to perform well. And this is precisely what
> drove me to look at avoiding going back to userspace in the first place.
>

We're not buffering any packets. What we lack is a way to tell the
guest that we're done processing all packets in the ring (IOW, re-enable
notifications).

--
error compiling committee.c: too many arguments to function



\
 
 \ /
  Last update: 2009-04-02 13:51    [W:0.103 / U:0.280 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site