• Linus Torvalds's avatar
    vfs: optimize inode cache access patterns · 3ddcd056
    Linus Torvalds authored
    The inode structure layout is largely random, and some of the vfs paths
    really do care.  The path lookup in particular is already quite D$
    intensive, and profiles show that accessing the 'inode->i_op->xyz'
    fields is quite costly.
    We already optimized the dcache to not unnecessarily load the d_op
    structure for members that are often NULL using the DCACHE_OP_xyz bits
    in dentry->d_flags, and this does something very similar for the inode
    ops that are used during pathname lookup.
    It also re-orders the fields so that the fields accessed by 'stat' are
    together at the beginning of the inode structure, and roughly in the
    order accessed.
    The effect of this seems to be in the 1-2% range for an empty kernel
    "make -j" run (which is fairly kernel-intensive, mostly in filename
    lookup), so it's visible.  The numbers are fairly noisy, though, and
    likely depend a lot on exact microarchitecture.  So there's more tuning
    to be done.
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
stat.c 10.6 KB