Re: [Xen-devel] QLogic Fibre Channel HBA Support

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> On Tue, Jul 06, 2004 at 03:23:47AM +0000, Brian Wolfe wrote:
> > Well, after having to restart another of the domains on that xen
> > server I discovered that the last in the list is the one that would
> > lock up once every 24 hours. (not certain fo the exact timeframe since
> > it locks during the night.)
> > 
> > I've disabled the cron entries that generate high workload to
> > eliminate that as a possible cause. 
> 
> This may do it -- once I told my beta users that high workloads and/or
> lots of entropy use could cause hangs, they started nice'ing and
> --bwlimit'ing their ssh rsyncs, and there hasn't been a hang for a few
> weeks.  No proof whether I was hitting another entropy bug or just
> workload.  (Reminder to lurkers -- I'm running 1.2 with /dev/random
> major,minor set to 1,9 -- same as /dev/urandom.)
> 
> > Next is to try running the virtual server on another xen host that is
> > running an older version of xen and xenolinux, see if that still hangs
> > it.
> 
> I think it should get worse if it changes at all.  Your /dev/random is
> 1,8, right?

If you use /dev/urandom (1,9) then you will never block while reading
entropy. The /only/ time anything can block while extracting entropy is
when a user application reads from /dev/random (1,8).

If you've linked /dev/random -> /dev/urandom then any lockups must be
due to bugs elsewhere. 

Compare:
 while [ true ] ; do dd if=/dev/urandom of=/dev/null bs=512 count=1024 
2>/dev/null && echo -n "." ; done
 while [ true ] ; do dd if=/dev/random of=/dev/null bs=512 count=1024 
2>/dev/null && echo -n "." ; done

 -- Keir


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