question about --bwlimit=

Paul Slootman paul at
Wed May 26 07:42:55 GMT 2004

On Mon 24 May 2004, Wayne Davison wrote:

> output.  Finally, I applied a modified version of the patch that Paul
> just reminded us that Debian is using, though I decided to limit the
> write size to "bwlimit * 512" rather than "bwlimit * 100" (at least for
> now, but feel free to argue that a different value is better).

What is a typical value for "len-total"? If it's typically less than a
couple of k, then bwlimit * 512 is a bit big, meaning that the patch
there will do mostly nothing...

I think the 100 was chosen because the point of this patch was to
prevent bursts of writing, and then waiting for buffers to drain. If you
have a 512kbit link, you typically don't want writes of more than
5kbytes if you want to also use the link interactively, it will take
0.1s for 5kB to go over the line (ignoring overhead). So if I start a
transfer with --bwlimit=40, I'd expect to still be able to use an
interactive ssh session over the same line without big delays. 40*512
means writes of 20k, meaning my keystrokes will take almost half a
second to go out if one of these writes have just been done. With 40*100
writes are 4kB, still much more than the typical MTU, and the max. delay
should be less than one tenths of a second.

So my vote is still for 100.

Paul Slootman

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