Subj : Re: Optimizing for latency
To   : comp.programming.threads
From : scream29125
Date : Tue Jun 07 2005 01:09 pm

Sorry, I forgot to mention that synchronization between the CPU and the
devices is interrupt-driven. This is why the CPU is idle most of the
time when it is waiting for the device to respond.

Additional info:

In setup #2, to verify my code, I forced the devices to be active only
one at a time (only 1 thread running at a time), jobs take 100-200ms
each. This is the same timing I get in setup #1 too. However when I
allow 4 devices to run concurrently (4 threads active) in setup #2,
jobs take 200-400ms.

By the way, this is a Xeon processor, and I have turned on
hyperthreading. I did not observe any timing differences with/without
hyperthreading.

.