[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: [Xen-devel] network hang trigger


  • To: "Bin Ren" <br260@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
  • From: "James Harper" <JamesH@xxxxxxxxxxxxxxxx>
  • Date: Thu, 16 Sep 2004 12:32:22 +1000
  • Delivery-date: Thu, 16 Sep 2004 03:35:20 +0100
  • List-id: List for Xen developers <xen-devel.lists.sourceforge.net>
  • Thread-index: AcSbgCTA5ZH4G8YFQH2wMIUUuQepsAABJJVgAAP9DmA=
  • Thread-topic: [Xen-devel] network hang trigger

This lends weight to my idea that it might be a timing related deadlock,
I put some debug statements in to see just how often the drop: path was
called in network_start_xmit (never), and now I almost can't get it to
fail. I put printk's in at the start of the function, and before both
the returns.

This particular machine is not SMP btw. It is a single CPU PII running
at 350Mhz (697 bogomips)

James

> -----Original Message-----
> From: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
> admin@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of James Harper
> Sent: Thursday, 16 September 2004 10:48
> To: Bin Ren; xen-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: RE: [Xen-devel] network hang trigger
> 
> This patch makes no difference on my system. Looking at the line
numbers
> in your patch, your netfront.c appears to be a different vintage to
> mine. I applied the patch manually and then rebuilt the xenU kernel
and
> then booted a domain with it. I haven't touched xen0. Is this the
> correct thing to be doing?
> 
> Ping >mtu from xenU to xen0 causes the network to hang immediately.
> Ping >mtu from xen0 to xenU sometimes causes the network to hang, but
> not always. 'ping -i 0.1 -s 6000 <xenU ip>' will mostly cause the hang
> in under 30 iterations.
> 
> The recovery time appears to be in the order of 60 seconds or so, with
a
> partial recovery and then relapse at about 30 seconds.
> 
> When I was thinking about this problem, I was imagining a deadlock
> condition where rapid back to back packets (eg a fragmented icmp
packet
> from ping or a fragmented udp packet from nfs) was causing a hang
until
> part of the deadlock timed itself out and the packets started flowing
> again. I couldn't see 1 packet causing a buffer exhaustion unless it
got
> itself into a loop where it kept retrying to send the second fragment
> and didn't free the buffer each time, but even then the buffer bug
would
> be a side effect.
> 
> The deadlock would have to be caused in the transmit from xenU to
xen0,
> and something about the difference between sending a ping and
responding
> to a ping is the difference between always causing a lockup and only
> sometimes causing a lockup.
> 
> Maybe we're seeing different manifestations of the same problem?
> 
> James
> 
> > -----Original Message-----
> > From: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
> > admin@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Bin Ren
> > Sent: Thursday, 16 September 2004 09:54
> > To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] network hang trigger
> >
> > I've just modified the netfront.c (haven't touched netback.c yet).
> I've
> > done two modifications: (1) free sk_buff properly on the transmit
path
> (2)
> > In netif_poll(...) function, packets **should not** be passed to
> > netif_rx(); instead, use: int netif_receive_skb(struct sk_buff
*skb).
> >
> > With these two modifications, under 'ping -s 6000', network only
> > occasionally loses a few packets but *very soon* recovers. It's much
> more
> > stable than before. I'll take a closer look at netfront.c and
> netback.c
> > tomorrow.
> >
> > Here is the patch. Please try it out. With your results, the changes
> may
> > get pushed into the repository.
> >
> 
> 
> -------------------------------------------------------
> This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170
> Project Admins to receive an Apple iPod Mini FREE for your judgement
on
> who ports your project to Linux PPC the best. Sponsored by IBM.
> Deadline: Sept. 24. Go here: http://sf.net/ppc_contest.php
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.sourceforge.net/lists/listinfo/xen-devel



-------------------------------------------------------
This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170
Project Admins to receive an Apple iPod Mini FREE for your judgement on
who ports your project to Linux PPC the best. Sponsored by IBM.
Deadline: Sept. 24. Go here: http://sf.net/ppc_contest.php
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.