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| author | Al Viro <viro@zeniv.linux.org.uk> | 2021-04-26 05:46:09 +0200 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2021-06-10 17:45:16 +0200 |
| commit | 7a1bcb5d255d4fd8b9725c3cf7ee0880a6369d2f (patch) | |
| tree | 61043b81e93a2e718ee69302688d2e122133dff5 /lib | |
| parent | iterate_and_advance(): get rid of magic in case when n is 0 (diff) | |
| download | linux-7a1bcb5d255d4fd8b9725c3cf7ee0880a6369d2f.tar.xz linux-7a1bcb5d255d4fd8b9725c3cf7ee0880a6369d2f.zip | |
iov_iter: massage iterate_iovec and iterate_kvec to logics similar to iterate_bvec
Premature optimization is the root of all evil... Trying
to unroll the first pass through the loop makes it harder
to follow and not just for readers - compiler ends up
generating worse code than it would on a "non-optimized"
loop.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/iov_iter.c | 91 |
1 files changed, 36 insertions, 55 deletions
diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 763114a754c5..2098059da64c 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -16,55 +16,44 @@ #define PIPE_PARANOIA /* for now */ -#define iterate_iovec(i, n, __v, __p, skip, STEP) { \ - size_t left; \ - size_t wanted = n; \ - __p = i->iov; \ - __v.iov_len = min(n, __p->iov_len - skip); \ - if (likely(__v.iov_len)) { \ - __v.iov_base = __p->iov_base + skip; \ - left = (STEP); \ - __v.iov_len -= left; \ - skip += __v.iov_len; \ - n -= __v.iov_len; \ - } else { \ - left = 0; \ - } \ - while (unlikely(!left && n)) { \ - __p++; \ - __v.iov_len = min(n, __p->iov_len); \ - if (unlikely(!__v.iov_len)) \ - continue; \ - __v.iov_base = __p->iov_base; \ - left = (STEP); \ - __v.iov_len -= left; \ - skip = __v.iov_len; \ - n -= __v.iov_len; \ - } \ - n = wanted - n; \ +#define iterate_iovec(i, n, __v, __p, skip, STEP) { \ + size_t left; \ + size_t wanted = n; \ + __p = i->iov; \ + do { \ + __v.iov_len = min(n, __p->iov_len - skip); \ + if (likely(__v.iov_len)) { \ + __v.iov_base = __p->iov_base + skip; \ + left = (STEP); \ + __v.iov_len -= left; \ + skip += __v.iov_len; \ + n -= __v.iov_len; \ + if (skip < __p->iov_len) \ + break; \ + } \ + __p++; \ + skip = 0; \ + } while (n); \ + n = wanted - n; \ } -#define iterate_kvec(i, n, __v, __p, skip, STEP) { \ - size_t wanted = n; \ - __p = i->kvec; \ - __v.iov_len = min(n, __p->iov_len - skip); \ - if (likely(__v.iov_len)) { \ - __v.iov_base = __p->iov_base + skip; \ - (void)(STEP); \ - skip += __v.iov_len; \ - n -= __v.iov_len; \ - } \ - while (unlikely(n)) { \ - __p++; \ - __v.iov_len = min(n, __p->iov_len); \ - if (unlikely(!__v.iov_len)) \ - continue; \ - __v.iov_base = __p->iov_base; \ - (void)(STEP); \ - skip = __v.iov_len; \ - n -= __v.iov_len; \ - } \ - n = wanted; \ +#define iterate_kvec(i, n, __v, __p, skip, STEP) { \ + size_t wanted = n; \ + __p = i->kvec; \ + do { \ + __v.iov_len = min(n, __p->iov_len - skip); \ + if (likely(__v.iov_len)) { \ + __v.iov_base = __p->iov_base + skip; \ + (void)(STEP); \ + skip += __v.iov_len; \ + n -= __v.iov_len; \ + if (skip < __p->iov_len) \ + break; \ + } \ + __p++; \ + skip = 0; \ + } while (n); \ + n = wanted - n; \ } #define iterate_bvec(i, n, __v, __bi, skip, STEP) { \ @@ -123,10 +112,6 @@ const struct iovec *iov; \ struct iovec v; \ iterate_iovec(i, n, v, iov, skip, (I)) \ - if (skip == iov->iov_len) { \ - iov++; \ - skip = 0; \ - } \ i->nr_segs -= iov - i->iov; \ i->iov = iov; \ } else if (iov_iter_is_bvec(i)) { \ @@ -141,10 +126,6 @@ const struct kvec *kvec; \ struct kvec v; \ iterate_kvec(i, n, v, kvec, skip, (K)) \ - if (skip == kvec->iov_len) { \ - kvec++; \ - skip = 0; \ - } \ i->nr_segs -= kvec - i->kvec; \ i->kvec = kvec; \ } else if (iov_iter_is_xarray(i)) { \ |