Re: [Nbd] performance

[Wouter Verhelst <w@...112...>]

On Fri, May 06, 2011 at 11:10:29AM +0200, Folkert van Heusden wrote:
> Hi,
>  
> I have a suggestion for performance enhancement of NBD.
> The idea is that between each request the client and server exchange a
> message.  Since networks are slow, this takes a while.

The current implementation works that way, because nbd-server is not
doing asynchronous reads, and therefore can only handle one request at a
time. But the protocol doesn't require it, and changing the
implementation so that it can handle one request while preparing to
handle another is what I meant with the performance improvements that I
mailed about earlier.

> Maybe we can, at least for write requests, send a couple of write
> commands with their data without immediately waiting for the reply and
> then if, say, 32 of them are send, wait for the acknowledgments.  If I
> remember correctly that's also how iSCSI does it.

There's no reason to limit them to write requests only. However read and
write requests do need to remain somewhat ordered, otherwise there are
going to be some issues.

-- 
The volume of a pizza of thickness a and radius z can be described by
the following formula:

pi zz a