On Tue, Oct 02, 2012 at 03:53:08AM +0200, Fredrik Tolf wrote: > Dear list, > > I'm having some problems with a Linux system using XFS filesystems, > on top of LVM, on top of mdraid, and I'm lacking ideas for how to > proceed with debugging it. The problem manifests itself in that > certain, simple I/O operations sometimes take extremely long to > complete -- not seldomly up to 20-30 seconds! What is a "simple IO operation"? > I used to have lesser problems of a similar kind previously, but > this extremeness only started showing up since I upgraded the system > from Debian Lenny (using Linux 2.6.26) to Squeeze (using 2.6.32). > I've since upgraded to 3.2.0, and now to 3.5.4, and they all exhibit > the same problem. > > The process having the worst problems with it usually sees them when > it calls upon Berkeley DB, the stack traces in which seems to tell > me that it's trying to do mmap'ed I/O in its region files, so I can > only assume that the stop happens when it's pulling in pages from > disk. I can't say I know for sure, but I'm getting the feeling that > it happens when some other process calls fdatasync() or somesuch > operation. I get this feeling because the problems very often seem > to happen exactly when I fetch a MySQL-backed webpage from the > system's HTTP server (at which point mysqld syncs its data to disk > after some session table update or the like). So is causing random 4k write IO? > Does anyone have any clue as to what might cause symptoms like > these, or, if not, how I can debug the issue further? Admittedly, > it's not as if I can be sure that the problem belongs with XFS > proper rather than LVM or mdraid, but I have to being somewhere. At > least XFS is the direct interface that my programs call before > getting stuck. :) More information about your setup needed and what is happening during the hangs: http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_when_reporting_a_problem.3F Also: ftrace or latencytop might point you at where the the latency is occurring. Then we might have some idea of what is causing it. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
