Re: [Nbd] strange delay of 5ms

[Goswin von Brederlow <goswin-v-b@...186...>]

Wouter Verhelst <w@...112...> writes:

> On Fri, Apr 22, 2011 at 02:31:23PM +0200, folkert wrote:
>> Hi,
>> 
>> I noticed something odd:
>> 
>> for(;;) {
>> 
>> 	// get timestamp in ms start
>> 
>> 	read(fd, size_of_nbd_request)
>> 
>> 	// get timestamp in ms end
>> 
>> 	printf("delay: %f\n", end - start);
>> 
>> 	// process request
>> }
>> 
>> Then, on a localhost-connection with:
>> dd if=/dev/zero of=/dev/nbd0
>> 
>> in this setup I noticed that it takes 5ms for the request header to come
>> in, but only when the processing takes a while.
>> What can be the cause of this?
>
> I'm not sure. I'm aware that nbd-server performance isn't exactly
> perfect, and I plan on working on that, but it would involve some
> significant work.

Could this be due to tcp corking? I.e. the kernel waiting for more data
to send in a single frame?

MfG
        Goswin