Re: benchmarking i/o throughput

Andreas Schäfer wrote:
> Hi,
> 
> I was curious how good openMosix' 2.6 I/O bandwith is, so I wrote to
> simple programs (see the attachment). The first one writes a
> configurable amount of data to the stdout and measures how long this
> takes. The second one simply reads data into a buffer.
> 
> When I connected both programs with a pipe and migrated only the
> reading process to another node I got a througput of approx. 6.3
> megabytes/s (on fast ethernet, both machine's CPUs loathing), which
> seemed to me pretty much ok.
> 
> The weird thing was that when migrating only the writing process, the
> throughput dropped to 90 kilobyte/s. I've also tried a much simpler C
> program which just printf'ed it's data to the stdout, but still the
> throughput was as low as before.
> 
> BTW: process migration causes the first sleep() in the writing
> program to return immediately, is this an expected behavior?

What happens if you replace
	std::cout.write(buf, BUF_SIZE);
with the syscall
	write(1, buf, BUF_SIZE);
C++ tends to break up writes into small pieces, so this could affect 
performance.


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