Re: [RFC PATCH] iov_iter: Convert iterate*() to inline funcs
From: David Howells <dhowells@redhat.com>
Date: 2023-08-11 17:08:22
Also in:
linux-fsdevel, linux-mm, lkml
Subsystem:
library code, the rest, userspace copyin/copyout (uiovec) · Maintainers:
Andrew Morton, Linus Torvalds, Alexander Viro
Linus Torvalds [off-list ref] wrote:
I like this generally, the code generation deprovement worries me a bit, but from a quick look on a test-branch it didn't really look all that bad (but the changes are too big to usefully show up as asm diffs)
Hmmm... It seems that using if-if-if rather than switch() gets optimised better in terms of .text space. The attached change makes things a bit smaller (by 69 bytes). David ---
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 8943ac25e202..f61474ec1c89 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c@@ -190,22 +190,18 @@ size_t iterate_and_advance(struct iov_iter *iter, size_t len, void *priv, if (unlikely(!len)) return 0; - switch (iov_iter_type(iter)) { - case ITER_UBUF: + if (likely(iter_is_ubuf(iter))) return iterate_ubuf(iter, len, priv, NULL, ustep); - case ITER_IOVEC: + if (likely(iter_is_iovec(iter))) return iterate_iovec(iter, len, priv, NULL, ustep); - case ITER_KVEC: + if (iov_iter_is_kvec(iter)) return iterate_kvec(iter, len, priv, NULL, step); - case ITER_BVEC: + if (iov_iter_is_bvec(iter)) return iterate_bvec(iter, len, priv, NULL, step); - case ITER_XARRAY: + if (iov_iter_is_xarray(iter)) return iterate_xarray(iter, len, priv, NULL, step); - case ITER_DISCARD: - iter->count -= len; - return len; - } - return 0; + iter->count -= len; + return len; } static __always_inline
@@ -217,22 +213,18 @@ size_t iterate_and_advance_csum(struct iov_iter *iter, size_t len, void *priv, if (unlikely(!len)) return 0; - switch (iov_iter_type(iter)) { - case ITER_UBUF: + if (likely(iter_is_ubuf(iter))) return iterate_ubuf(iter, len, priv, csum, ustep); - case ITER_IOVEC: + if (likely(iter_is_iovec(iter))) return iterate_iovec(iter, len, priv, csum, ustep); - case ITER_KVEC: + if (iov_iter_is_kvec(iter)) return iterate_kvec(iter, len, priv, csum, step); - case ITER_BVEC: + if (iov_iter_is_bvec(iter)) return iterate_bvec(iter, len, priv, csum, step); - case ITER_XARRAY: + if (iov_iter_is_xarray(iter)) return iterate_xarray(iter, len, priv, csum, step); - case ITER_DISCARD: - iter->count -= len; - return len; - } - return 0; + iter->count -= len; + return len; } static size_t copy_to_user_iter(void __user *iter_to, size_t progress,