Re: [9fans] network throughput measurements

[presotto@plan9.bell-labs.com]

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>actually we were more interested in measuring the latency p9 imposes
>on transmission, i.e.  the time it takes for the first byte to start
>appearing on the network...

+

>	buf = mallocz(i, 1);
>	tbegin = nsec();
>	for(j = 0; j < 10000; j++)
>		write(fd, buf, i);
>	tend = nsec();

I'm not complaining, I like seeing numbers.  However, these two statements
don't jibe.

> at one point the receiver side was printing the total number of bytes
> received, which was in line with calculations, so no huge discrepancy
> there..

I'm actually interested in the number of bytes/packet seen on the receiver.
All you measured what the amount of time to queue the messages on the
sender, not the time to send them, the average time for each byte to make
the journey, or the time to get the first byte to the wire.  If all you
want to do to improve the numbers for plan 9, we can do it trivially by
just making sure we buffer all the 1 byte writes before sending anything
 out.  Then you're just measuring the time for 10000 1 byte writes which is
moderately quick.  However, I suspect that's not what you want to speed
up.  I suspect that the BSD stack is doing significantly better than we are
at ganging bytes/packet and hence causes fewer interrupts, runs up the IP
stack, system calls, etc.

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From: andrey mirtchovski <andrey@lanl.gov>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] network throughput measurements
Date: Fri, 8 Mar 2002 14:29:03 -0700
Message-ID: <20020308212840.DEFC61999B@mail.cse.psu.edu>

actually we were more interested in measuring the latency p9 imposes
on transmission, i.e.  the time it takes for the first byte to start
appearing on the network...

yes, this is not the best way to measure performance, but it was a
good exercise before porting netpipe natively to p9.  the results
seemed interesting enough to "publish" :)

at one point the receiver side was printing the total number of bytes
received, which was in line with calculations, so no huge discrepancy
there..

andrey