Hello, On 08/19/2010 10:53 AM, Christoph Hellwig wrote: > On Wed, Aug 18, 2010 at 07:07:34PM -0700, Darrick J. Wong wrote: >> Oddly, I ran the entire suite of tests against a larger set of machines, and >> with Tejun's RFC patchset I didn't see nearly as much of an improvement. I >> have been trying to put together a new tree based on "replace barrier with >> sequenced flush" and Christoph's "explicitly flush/FUA" patch sets, though I've >> gotten lost in the weeds. :( > > Tejun's patches don't allow concurrent cache flushes to happen, while > my patch did. Tejun said there are drivers that can't handly empty > flushes with a bio attached, making this nessecary. > > Tejun, any idea what drivers that would be? What was the configuration? If dm was involved, both md and dm can only process single flush request at a time. Supporing multiple flushes in flight wouldn't be too difficult. It's just the way things are implemented with the previous barrier implementation. It can definitely be improved. >> I also experienced some sort of crash with Tejun's relaxed barrier >> patch on one of my systems. I was hitting the BUG_ON in >> drivers/scsi/scsi_lib.c, line 1115. > > My kernel source doesn't have a BUG_ON line there, but only one two > lines above. A req->nr_phys_segments that's zero sounds a bit like > empty flush requests, I'll need to look into it again. Yeah, definitely sounds like REQ_FS|REQ_FLUSH request causing problem. Can you post the kernel log? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
