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Re: [libvirt] [PATCH 0/6] Allow debug dump in case of crashes



On Thu, Mar 03, 2011 at 10:00:14PM +0800, Daniel Veillard wrote:
> On Thu, Mar 03, 2011 at 11:48:51AM +0000, Daniel P. Berrange wrote:
> > On Thu, Mar 03, 2011 at 06:26:19PM +0800, Daniel Veillard wrote:
> > > Something like killall -USR2 libvirtd allows to see the
> > > kind of output one get, an idle libvirtd is quiet, but
> > > handle/timer/fdpolls tend to be very verbose, maybe we need
> > > an intermediate debug level, but that would also impact the
> > > API. Maybe now that this part is well debugged some of those
> > > could be suppressed or commented off.
> > > 
> > > Also the buffer is a statically allocated 64KB, maybe this
> > > could be made more flexible but IMHO that's not fundamental.
> > 
> > 64 KB is unlikely to be sufficiently large if libvirt is running
> > under RHEV with moderate load. With a fairly strict log filter
> > of '1:libvirt 1:util 1:qemu' RHEV generates > 300 MB of logs
> > in ~10 minutes. This works out at approx 512 KB per second so
> > a 64 KB buffer will only capture 125 milliseconds at that log
> > filter level, and far far less if collecting full debug logs
> 
>   yeah, I was afraid of this kind of scenarios, and went for the minimal
> approach since the static buffer is already in the current code. Problem
> is that I don't think we should really rely on an user provided value,
> and getting a dynamic algorithm (keep say at least one second worth of
> log) sounds hard to implement right. I was somehow hoping that some of
> the background noises could be reduced by further patches. Another
> option would be to apply a specific filter (which could be empty by
> default) for the debug buffer, and that is rather trivial to implement.

We could make a configurable in libvirtd.conf for buffer size. eg to
set a 1 MB ringbuffer, users could do:

  log_ringbuffer = 1048576

Regards,
Daniel
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