netdev - Re: Receive side performance issue with multi-10-GigE and NUMA

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Date:	Fri, 21 Aug 2009 11:23:41 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Bill Fink <billfink@...dspring.com>
Cc:	Linux Network Developers <netdev@...r.kernel.org>, brice@...i.com,
	gallatin@...i.com
Subject: Re: Receive side performance issue with multi-10-GigE and NUMA

On Fri, Aug 21, 2009 at 12:14:21AM -0400, Bill Fink wrote:
> On Thu, 20 Aug 2009, Neil Horman wrote:
> 
> > On Thu, Aug 20, 2009 at 03:50:44AM -0400, Bill Fink wrote:
> > 
> > > When I tried an actual nuttcp performance test, even when rate limiting
> > > to just 1 Mbps, I immediately got a kernel oops.  I tried to get a
> > > crashdump via kexec/kdump, but the kexec kernel, instead of just
> > > generating a crashdump, fully booted the new kernel, which was
> > > extremely sluggish until I rebooted it through a BIOS re-init,
> > > and never produced a crashdump.  I tried this several times and
> > > an immediate kernel oops was always the result (with either a TCP
> > > or UDP test).  A ping test of 1000 9000-byte packets with an interval
> > > of 0.001 seconds (which is 72 Mbps for 1 second) on the other hand
> > > worked just fine.
> > 
> > The sluggishness is expected, since the kdump kernel operates out of such
> > limited memory.  don't know why you booted to a full system rather than did a
> > crash recovery.  Don't suppose you got a backtrace did you?
> 
> There was a backtrace on the screen but I didn't have a chance to
> record it.  BTW did anyone ever think to print the backtrace in
> reverse (first to some reserved memory and then output to the display)
> so the more interesting parts wouldn't have scrolled off the top of
> the screen?
> 
The real solution is to use a console to which the output doesn't scroll off the
screen.  Normally people use a serial console they can log, or a RAC card that
they can record. Even on a regular vga monitor in text mode, you can set up the
vt iirc to allow for scrolling.

Neil

> 						-Bill
> 
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