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| author | Mateusz Guzik <mjguzik@gmail.com> | 2023-08-12 19:15:54 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2023-08-12 19:18:47 +0300 |
| commit | c8afaa1b0f8bc93d013ab2ea6b9649958af3f1d3 (patch) | |
| tree | cdf2d4c2f22ab40d7d31ba99ffdce18e3dfcc6cd /include/linux/prefetch.h | |
| parent | 3feecb1b848359b152dd66b26c24c2454a64fc15 (diff) | |
| download | linux-c8afaa1b0f8bc93d013ab2ea6b9649958af3f1d3.tar.xz | |
locking: remove spin_lock_prefetch
The only remaining consumer is new_inode, where it showed up in 2001 as
commit c37fa164f793 ("v2.4.9.9 -> v2.4.9.10") in a historical repo [1]
with a changelog which does not mention it.
Since then the line got only touched up to keep compiling.
While it may have been of benefit back in the day, it is guaranteed to
at best not get in the way in the multicore setting -- as the code
performs *a lot* of work between the prefetch and actual lock acquire,
any contention means the cacheline is already invalid by the time the
routine calls spin_lock(). It adds spurious traffic, for short.
On top of it prefetch is notoriously tricky to use for single-threaded
purposes, making it questionable from the get go.
As such, remove it.
I admit upfront I did not see value in benchmarking this change, but I
can do it if that is deemed appropriate.
Removal from new_inode and of the entire thing are in the same patch as
requested by Linus, so whatever weird looks can be directed at that guy.
Link: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/fs/inode.c?id=c37fa164f793735b32aa3f53154ff1a7659e6442 [1]
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/prefetch.h')
| -rw-r--r-- | include/linux/prefetch.h | 7 |
1 files changed, 1 insertions, 6 deletions
diff --git a/include/linux/prefetch.h b/include/linux/prefetch.h index b83a3f944f28..b068e2e60939 100644 --- a/include/linux/prefetch.h +++ b/include/linux/prefetch.h @@ -25,11 +25,10 @@ struct page; prefetch() should be defined by the architecture, if not, the #define below provides a no-op define. - There are 3 prefetch() macros: + There are 2 prefetch() macros: prefetch(x) - prefetches the cacheline at "x" for read prefetchw(x) - prefetches the cacheline at "x" for write - spin_lock_prefetch(x) - prefetches the spinlock *x for taking there is also PREFETCH_STRIDE which is the architecure-preferred "lookahead" size for prefetching streamed operations. @@ -44,10 +43,6 @@ struct page; #define prefetchw(x) __builtin_prefetch(x,1) #endif -#ifndef ARCH_HAS_SPINLOCK_PREFETCH -#define spin_lock_prefetch(x) prefetchw(x) -#endif - #ifndef PREFETCH_STRIDE #define PREFETCH_STRIDE (4*L1_CACHE_BYTES) #endif |