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    SubjectRe: [PATCH 10/25] Unionfs: add un/likely conditionals on copyup ops
    Erez Zadok wrote:
    > Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
    > ---
    > fs/unionfs/copyup.c | 102 +++++++++++++++++++++++++-------------------------
    > 1 files changed, 51 insertions(+), 51 deletions(-)
    >
    > diff --git a/fs/unionfs/copyup.c b/fs/unionfs/copyup.c
    > index 23ac4c8..e3c5f15 100644
    > --- a/fs/unionfs/copyup.c
    > +++ b/fs/unionfs/copyup.c
    > @@ -36,14 +36,14 @@ static int copyup_xattrs(struct dentry *old_lower_dentry,
    >
    > /* query the actual size of the xattr list */
    > list_size = vfs_listxattr(old_lower_dentry, NULL, 0);
    > - if (list_size <= 0) {
    > + if (unlikely(list_size <= 0)) {


    I've been told several times that adding these is almost always bogus - either it
    messes up the CPU branch prediction or the compiler/CPU just does a lot better at
    finding the right way without these hints.

    Adding them as a blanket seems rather strange. Have you got any numbers that this
    really improves performance?

    Auke
    -
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