Re: [PATCH v2 05/11] md/raid5: add scribble region for buffer lists

[Jody McIntyre <scjody@sun.com>]

On Fri, Jun 05, 2009 at 12:19:07PM -0700, Dan Williams wrote:
> One of the design goals was to prevent the occurrence of the
> softlockup watchdog events which seem to trigger on large raid6
> resyncs.  A per-cpu scheme would still require preempt_disable() while
> the calculation is active, so perhaps we just need a call to
> cond_resched() in raid5d to appease the scheduler.

FWIW we added this to the patches shipped with Lustre:

Index: linux-2.6.18-128.1.1/drivers/md/raid5.c
===================================================================
--- linux-2.6.18-128.1.1.orig/drivers/md/raid5.c
+++ linux-2.6.18-128.1.1/drivers/md/raid5.c
@@ -2987,6 +2987,8 @@ static void raid5d (mddev_t *mddev)
 		handle_stripe(sh, conf->spare_page);
 		release_stripe(sh);
 
+		cond_resched();
+
 		spin_lock_irq(&conf->device_lock);
 	}
 	PRINTK("%d stripes handled\n", handled);

I thought most of these issues were gone in more recent kernels, but we
haven't tested RAID on anything other than RHEL 4+5 extensively (Lustre
doesn't support sufficiently new kernels yet.)

Cheers,
Jody