This is a note to let you know that I've just added the patch titled
NFSD: Remove be32_to_cpu() from DRC hash function
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nfsd-remove-be32_to_cpu-from-drc-hash-function.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 46beb937a204dd62755493cc7c9e394257a18afc
Author: Chuck Lever <chuck.lever@xxxxxxxxxx>
Date: Thu Sep 30 19:10:03 2021 -0400
NFSD: Remove be32_to_cpu() from DRC hash function
[ Upstream commit 7578b2f628db27281d3165af0aa862311883a858 ]
Commit 7142b98d9fd7 ("nfsd: Clean up drc cache in preparation for
global spinlock elimination"), billed as a clean-up, added
be32_to_cpu() to the DRC hash function without explanation. That
commit removed two comments that state that byte-swapping in the
hash function is unnecessary without explaining whether there was
a need for that change.
On some Intel CPUs, the swab32 instruction is known to cause a CPU
pipeline stall. be32_to_cpu() does not add extra randomness, since
the hash multiplication is done /before/ shifting to the high-order
bits of the result.
As a micro-optimization, remove the unnecessary transform from the
DRC hash function.
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index 6e0b6f3148dca..a4a69ab6ab280 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -87,7 +87,7 @@ nfsd_hashsize(unsigned int limit)
static u32
nfsd_cache_hash(__be32 xid, struct nfsd_net *nn)
{
- return hash_32(be32_to_cpu(xid), nn->maskbits);
+ return hash_32((__force u32)xid, nn->maskbits);
}
static struct svc_cacherep *
