On 01/05/2011 12:44 AM, Christopher Smith wrote:
Yes, my C program can reach 100MB/s or even 110MB/s when writing data to
the
disk sequentially, but with direct I/O enabled, the maximal throughput is
about
140MB/s. But the biggest difference is CPU usage.
Without direct I/O, operating system uses a lot of CPU time (the data below
is
got with top, and this is a dual-core processor with hyperthread enabled).
Cpu(s): 3.4%us, 32.8%sy, 0.0%ni, 50.0%id, 12.1%wa, 0.0%hi, 1.6%si,
0.0%st
But with direct I/O, the system time can be as little as 3%.
I'm surprised that system time is really that high. We did Atom experiments
where it wasn't even close to that. Are you using a memory mapped file? If
not are you buffering your writes? Is there perhaps
something dysfunctional about the drive controller/driver you are using?
Which Atom processor did you use? Could you tell me how you did your
experiment?
Best,
Da
