On Fri, Jul 02, 2010 at 03:23:17AM +1000, Nick Piggin wrote: > On Wed, Jun 30, 2010 at 10:40:49PM +1000, Nick Piggin wrote: > > But actually it's not all for scalability. I have some follow on patches > > (that require RCU inodes, among other things) that actually improve > > single threaded performance significnatly. git diff workload IIRC was > > several % improved from speeding up stat(2). > > I rewrote the store-free path walk patch that goes on top of this > patchset (it's now much cleaner and more optimised, I'll post a patch > soonish). It is quicker than I remembered. > > A single thread running stat(2) in a loop on a file "./file" has the > following cost (on an 2s8c Barcelona): > > 2.6.35-rc3 595 ns/op > patched 336 ns/op > > stat(2) takes 56% the time with patches. It's something like 13 fewer > atomic operations per syscall. > > What's that good for? A single threaded, cached `git diff` on the linux > kernel tree takes just 81% of the time after the vfs patches (0.27s vs > 0.33s). At the other end of the scale, I tried dbench on ramfs on the little 32n64c Altix. Dbench actually has statfs() call completely removed from the workload -- it's still a little problematic and patched kernel throughput is ~halved with statfs(). dbench procs 1 64 2.6.35-rc3 235MB/s 95MB/s ( 0.6% scaling) patched 245MB/s 14870MB/s (94.8% scaling) (note all these numbers are with store-free path walking patches on top of the posted patchset -- dbench procs do path walking from common cwds so it will never scale this well if we have to take refcounts on common dentries) Thanks, Nick -- 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
