Rsync performance increase through buffering

Dave Dykstra dwd at
Wed Dec 11 21:22:01 EST 2002

On Sun, Dec 08, 2002 at 11:48:57PM -0800, Craig Barratt wrote:
> I've been studying the read and write buffering in rsync and it turns
> out most I/O is done just a couple of bytes at a time.  This means there
> are lots of system calls, and also most network traffic comprises lots
> of small packets.  The behavior is most extreme when sending/receiving
> file deltas of identical files.
> Below is a patch to a few files that adds read and write buffering in
> the places where the I/O was unbuffered, adds buffering to write_file()
> and removes the unneeded gettimeofday() system call in show_progress().
> However, on a network test doing a send from cygwin/WinXP to rsyncd
> on rh-linux the running time improves from about 700 seconds to 215
> seconds (with a cpu load of around 17% versus 58%, if you believe
> cygwin's cpu stats).  This is probably an extreme case since the system
> call penalty in cygwin is high.  But I would suspect a significant
> improvement is possible with a slow network connection, since a lot
> less data is being sent.

Looks like a good candidate for the "patches" directory now and for
integration in 2.6.0.

- Dave

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