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NFSD: Remove be32_to_cpu() from DRC hash function

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Commit 7142b98d9f ("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>
This commit is contained in:
Chuck Lever 2021-09-30 19:10:03 -04:00
parent 23a1a573c6
commit 7578b2f628
1 changed files with 1 additions and 1 deletions
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2
fs/nfsd/nfscache.c
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@ -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 *