On Wed, Feb 23, 2011 at 11:24:50AM -0500, Martin K. Petersen wrote: > >>>>> "Dave" == Dave Chinner <david@xxxxxxxxxxxxx> writes: > > >> Agreed. I too am curious to study which circumstances favor copying > >> vs blocking. > > Dave> IMO blocking is generally preferable in high throughput threaded > Dave> workloads as there is always another thread that can do useful > Dave> work while we wait for IO to complete. Most use cases for DIF > Dave> center around high throughput environments.... > > Yeah. > > A while back I did a bunch of tests with a liberal amount of > wait_on_page_writeback() calls added to (I think) ext2, ext3, and > XFS. For my regular workloads there was no measurable change (kernel > builds, random database and I/O tests). I'm sure we'll unearth some apps > that will suffer when DI is on but so far I'm not too worried about > blocking in the data path. > > My main concern is wrt. metadata because that's where extN really > hurts. Simple test: Unpack a kernel tarball and watch the directory > block fireworks. Given how frequently those buffers get hit I'm sure > blocking would cause performance to tank completely. I looked into > fixing this in ext2 but I had to stop because my eyes were bleeding. Not problems with metadata modifications for XFS - all metadata IO is done with a lock held preventing modifications while IO is in progress. 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
