5.15-stable review patch. If anyone has any objections, please let me know.
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From: Chuck Lever chuck.lever@oracle.com
[ 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@oracle.com --- fs/nfsd/nfscache.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c index 6b9ef15c9c03b..a838909502907 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 *