On Mon, Sep 20, 2010 at 05:17:26PM -0500, Shawn Bohrer wrote: > Thanks Dave for your explanations. > > On Mon, Sep 20, 2010 at 10:05:35AM +1000, Dave Chinner wrote: > > FWIW, if you can work out the magic necessary (perhaps systemtap) it > > woul dbe really interesting to know whether it is the same buffer > > that is causing the latency every time (i.e. get the bp->b_bn field > > from the metadata buffer). With the block number, we can use xfs_db > > to dig out what the buffer actually is.... > > I'm working on a dev box right now so I just added a trace_printk() to > print out the bp->b_bn field when the xfs_buf_lock blocks for more > than 300ms. Here are some numbers (I can easily get a lot more): > > _xfs_buf_find: xfs_buf_lock blocked for 1843ms on bp->b_bn: 812730376 > _xfs_buf_find: xfs_buf_lock blocked for 1504ms on bp->b_bn: 406702514 > _xfs_buf_find: xfs_buf_lock blocked for 307ms on bp->b_bn: 881190896 > _xfs_buf_find: xfs_buf_lock blocked for 433ms on bp->b_bn: 406703400 > _xfs_buf_find: xfs_buf_lock blocked for 420ms on bp->b_bn: 541595968 > _xfs_buf_find: xfs_buf_lock blocked for 308ms on bp->b_bn: 44945968 > _xfs_buf_find: xfs_buf_lock blocked for 702ms on bp->b_bn: 406027744 > _xfs_buf_find: xfs_buf_lock blocked for 454ms on bp->b_bn: 474486504 > _xfs_buf_find: xfs_buf_lock blocked for 869ms on bp->b_bn: 881195976 > _xfs_buf_find: xfs_buf_lock blocked for 387ms on bp->b_bn: 1287891544 > _xfs_buf_find: xfs_buf_lock blocked for 397ms on bp->b_bn: 1220116224 > _xfs_buf_find: xfs_buf_lock blocked for 461ms on bp->b_bn: 2101644280 > _xfs_buf_find: xfs_buf_lock blocked for 312ms on bp->b_bn: 338919728 > _xfs_buf_find: xfs_buf_lock blocked for 356ms on bp->b_bn: 1016769536 > _xfs_buf_find: xfs_buf_lock blocked for 593ms on bp->b_bn: 474488848 > _xfs_buf_find: xfs_buf_lock blocked for 323ms on bp->b_bn: 1022248984 > > I should say that not every one of these results in a stall in my > application, since my app needs to generate a page fault while that > lock is held. Hmmm - it would be good to know which one produced the latency, given there does not appear to be a pattern in the block numbers. > What do I need to do to convert the block numbers to a buffer? # xfs_db -r -c "daddr 812730376" -c "print" <dev> Will dump the sector at that address. That should be enough to tell us what is in the buffer (by the magic number). Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
