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    SubjectRe: [patch 00/52] vfs scalability patches updated
    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


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