Re: packet re-ordering on SMP machines.

["Xiaoliang \(David\) Wei" <weixl@caltech.edu>]

Hi Ben and Jamal,
       Are you guys sure that getdayoftime per packet is a big overhead on
Gbps connection?
       Do you compare the performance with getdayoftime per packet and
without? I guess RFC 1323 specifies that each packet should have a timestamp
(although not from getdayoftime).
       Also, what's your testbed's configuration, Ben? (I guess if we can
use faster hardware to overcome this effect...)
      Thank you:)

     ps: I am working on some high speed TCP experiment and may want to make
getdayoftime every packet...

-David
Xiaoliang (David) Wei             Graduate Student in CS@Caltech
http://www.cs.caltech.edu/~weixl
====================================================
----- Original Message -----
From: "Ben Greear" <greearb@candelatech.com>
To: "jamal" <hadi@cyberus.ca>
Cc: <netdev@oss.sgi.com>
Sent: Sunday, August 25, 2002 9:34 PM
Subject: Re: packet re-ordering on SMP machines.


>
> jamal wrote:
>
> > That doesnt sound impressive at all. I know it's about .8 of wire rate
> > but you should be able to exceed that.
> > Robert was generating in the range of 800Kpps with that NIC if i recall
> > corectly
>
> I had only tested 1514 byte pkts, so I was getting around 880Mbps,
> which is pretty good as far as I know.
>
> I see about 255 kpps when sending 64 byte pkts to myself.  Still
> dropping about 1 in 4000 packets at this speed.  I think most of Robert's
> tests didn't involve actually doing something with the received packet
> though, and I am inspecting it for latency, sequence number, etc.
>
> I'm even doing a __get_timeofday() call to calculate the latency...need
> to find a faster way to do that...
>
> If I only allocate/scan 1 per 100 packets (ie alloc one packet and send it
100 times),
> then I get a more respectable 365kpps.  Robert's patch should definately
help!
>
> > Also if you have SMP, tie each onto a CPU.
>
> That's with the irq_afinity thing in proc, right?
>
> > Additionaly get the skb recycler patch from Robert, it should improve
> > things even more.
>
> Do you happen to have a URL for this?
>
> Actually, the various network tweaks are relatively hard to find
> (at least to find the most up-to-date coppies).  It would be great if
> there was a place where they were all concentrated.
>
> >
> >
> >>Also, I see the hard_start_xmit call failing 5876 times out of 2719493
> >>calls (for example).  The code that calls the method looks like this:
> >>
> >
> >
> > I dont have access to that NIC. But a stoopid question: Have you tried
> > increasing the transmit queue via ifconfig? 1000 packets is reasonable
> > for gige.
>
> I upped it, but it didn't stop the errors.  The NIC is still performing,
> so it may not be a real problem...
>
> Thanks for the info,
> Ben
>
> --
> Ben Greear <greearb@candelatech.com>       <Ben_Greear AT excite.com>
> President of Candela Technologies Inc      http://www.candelatech.com
> ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear
>
>
>
>
>