On Tue, Feb 04, 2003 at 03:06:05AM +0200, Mikko Rauhala wrote:
> Hello
>
> I'm using a cable modem with a slow uplink, and therefore when I want to
> transfer large amounts of data upstream, I tend to use rsync with
> --bwlimit. However, the stock rsync seems to send a bit too much data at
> once for comfort, momentarily blocking my meager upstream enough to
> bother latency and downstream data transfer (through not getting through
> enough ack packets when rsync data fills the cabel modem buffer).
>
> I tried a quick kludge, simply limiting the size of a single write()
> operation so that the write/sleep cycle happens more often, yielding (I
> hoped) a more steady flow of data, so that the cabel modem buffer
> wouldn't contain too much data at any point. Through comparing
> interactive session use before and after the patch, I would have to
> conclude that this kludge worked in my Debian GNU/Linux (unstable) box.
>
> Now, the point is that I like the kludge and I'd like rsync proper to
> adopt perhaps a lesser-kludgeish command line option (or something) for
> this kind of functionality, if you're so inclined. Might be useful to
> others in similiar circumstances.
>
> Here's my quick kludge (just a one-liner really, thanks to a proper
> write loop structure), which probably can reduce performance in the
> general case through using more writes, but has worked nicely for me
> (against 2.5.5 from Debian's sources; and yes, the "1024" is a magic
> number):
Just how magic is the 1024? To what was bwlimit set? And
the MTU?
You do bring up an interesting point. I could see
restricting the write to bwlimit/100. Sleeping much longer
than 100ms is a bit crude.
something like
max_xmit = bwlimit / 100;
if (max_xmit < 1024) max_xmit = 1024;
and then in writefd_unbuffered
size_t n = len - total;
if (max_xmit && n > max_xmit) n = max_xmit;
I'm no network internals sorcerer (networking seems something
of a black art) and wouldn't want things to get too magical
but perhaps linking this into MTU or somewhat. I'd hate to
see us setting it to a value that causes lots of padded
packets.
>
> --- io.c.old 2002-03-22 07:14:44.000000000 +0200
> +++ io.c 2003-02-04 02:50:14.000000000 +0200
> @@ -440,7 +440,7 @@
> if (FD_ISSET(fd, &w_fds)) {
> int ret;
> size_t n = len-total;
> - ret = write(fd,buf+total,n);
> + ret = write(fd,buf+total,(n<1024?n:1024));
>
> if (ret == -1 && errno == EINTR) {
> continue;
>
> --
> Mikko Rauhala - [EMAIL PROTECTED] - <URL:http://www.iki.fi/mjr/>
> Transhumanist - WTA member - <URL:http://www.transhumanism.org/>
> Singularitarian - SIAI supporter - <URL:http://www.singinst.org/>
>
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