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Re: Writing to multiple descriptors with one system call

On Thu, 18 Mar 2010 21:36:47 +0100
Jean-Yves Migeon <> wrote:

> Pretty much all servers use the accept loop thing and fork/pthread right 
> after, but this was not my point.

High performance non-single-threaded servers often maintain a pool of
persistent processes or threads which accept(2) concurrently, either in
blocking mode or with polling (generally polling to allow listening to
multiple addresses/interfaces).  But indeed this doesn't change much
for this thread...

> Having 80% system time passed in write() calls is not negligeable, but 
> if you send the data byte after byte, I hardly see why it would be the 
> syscall's fault here. You will have to assess that the overhead does 
> indeed come from the context switch, and not by queuing up packets for 
> the PHY, block I/Os, or moving data around the IP stack. There is a big 
> mess behind a write(2), and the context switch is just one small part of 
> it. Instrument. "You can't control what you can't measure."


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