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

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.