Re: Issues with INET sockets through loopback (lo)

[Hans Henrik Happe <hhh@imada.sdu.dk>]

On Monday 23 May 2005 14:09, DervishD wrote:
> With 3-1 I get an usage of 20% more or less. But with 16-1 the
> CPU usage is nearly 0! and with 16-16 the usage is 5% more or less.

That even worse than what I have experienced.
  
> > I have tried more regular communication patterns but this gives full CPU 
> > utilization as expected. For instance sending messages in a ring (attach: 
> > ring-inet.c). 
> 
> Not here. It uses 29% instead of 20% with 3-1, but drops to 6%
> when using 16 processes. Far from full CPU usage. A test with 16-160
> doesn't make the system slower or irresponsive, at least here...

Again, even worse.
 
> Not here. I haven't noticed any slow-down or latency increase
> using high number of messages. Using 16-160 only uses at most 7% of
> CPU per process, and I don't feel the system irresponsive.

That's strange. Maybe I should try an AMD system myself. Btw the number of 
processes is an upper bound of the number of messages. This is just a 
simplification in the code.

> If you want more accurate results, try to modify your test
> programs: make them run for a couple of minutes (you decide how much
> time, the longer, the better) and kill all children processes. After
> that, use getrusage() (with RUSAGE_CHILDREN) or wait3(). That should
> give more accurate results.

I could do that, but my point is that kernel goes into the idle state even 
though there always should be a runable process. Your tests supports this.
I don't believe that more accuracy would help because it is quite clear that 
CPU is in the idle state.
 
> Hope that helps. If you want to make any other test, tell me.
> I'll try to help.

Thanx. Your tests actually confirms the first issue, which also is the one 
that I have been most concerned about. 

I hope that someone with knowledge of how this part of the kernel work can 
confirm that this is a problem with the kernel or explain why it is supposed 
to behave in this manor.

Hans Henrik Happe