On Tue, Sep 07, 2010 at 02:26:54PM +0200, Tejun Heo wrote: > On 09/07/2010 12:35 PM, Tejun Heo wrote: > > Can you please help me a bit more? Are you saying the following? > > > > Work w0 starts execution on wq0. w0 tries locking but fails. Does > > delay(1) and requeues itself on wq0 hoping another work w1 would be > > queued on wq0 which will release the lock. The requeueing should make > > w0 queued and executed after w1, but instead w1 never gets executed > > while w0 hogs the CPU constantly by re-executing itself. Also, how > > does delay(1) help with chewing up CPU? Are you talking about > > avoiding constant lock/unlock ops starving other lockers? In such > > case, wouldn't cpu_relax() make more sense? > > Ooh, almost forgot. There was nr_active underflow bug in workqueue > code which could lead to malfunctioning max_active regulation and > problems during queue freezing, so you could be hitting that too. I > sent out pull request some time ago but hasn't been pulled into > mainline yet. Can you please pull from the following branch and add > WQ_HIGHPRI as discussed before and see whether the problem is still > reproducible? Ok, it looks as if the WQ_HIGHPRI is all that was required to avoid the log IO completion starvation livelocks. I haven't yet pulled the tree below, but I've now created about a billion inodes without seeing any evidence of the livelock occurring. Hence it looks like I've been seeing two livelocks - one caused by the VM that Mel's patches fix, and one caused by the workqueue changeover that is fixed by the WQ_HIGHPRI change. Thanks for you insights, Tejun - I'll push the workqueue change through the XFS tree to Linus. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
