slow writes on nfs with bge devices

[Max Laier]

On Sunday 21 January 2007 13:25, Bruce Evans wrote:
> On Sun, 21 Jan 2007, Max Laier wrote:
> > On Sunday 21 January 2007 07:25, Bruce Evans wrote:
> >> nfs writes much less well with bge NICs than with other NICs (sk,
> >> fxp,
> >
> > Do you use hardware checksumming on the bge?  There is an XXX in
> > bge_start_locked() that looks a bit suspicious to me.
>
> I use the default for that.  Wouldn't checksum problems show up as
> errors somwhere?

Did you look at the code in question?  It is concerned with fragmented 
packet chains (which NFS over UDP usually generated) and only commits to 
sending them, if there are enough descriptors available at once.  This 
can easily explain burstyness.

Can you just try to disable the delayed checksums via "ifconfig -txcsum"?  
Should be an easy enough test.

> >>> [excessive quoting deleted]
>
> tcpdump shows a lot of intervals between nfs write requests of almost
> exactly 10 mS (even with HZ = 1000, but more obvious with HZ = 100)
> for the broken case, so the problem is apparently related to timeouts,
> or timeouts are masking a larger problem.  (The average interval
> between write requests needs to be about 683 uS to avoid wasting any
> bandwith. fxp <-> fxp on the same network averages 708 uS.  fxp <-> bge
> 5701 averages 3981.)

See above, I really think that there is something about that if_start loop 
that might be causing this.

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