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Subject: [PATCH v1 2/5] SUNRPC: Optimize xdr_reserve_space()
From:   Chuck Lever <chuck.lever@oracle.com>
To:     linux-nfs@vger.kernel.org
Date:   Sun, 05 Jun 2022 15:58:31 -0400
Message-ID: <165445911199.1664.12318094116152634589.stgit@bazille.1015granger.net>
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References: <165445865736.1664.4497130284832282034.stgit@bazille.1015granger.net>
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The xdr_get_next_encode_buffer() function is called infrequently.
On a typical build/test workload, it's called about 1 time in 400
calls to xdr_reserve_space() (measured on NFSD).

Force the compiler to remove it from xdr_reserve_space(), which is
a hot path. This change reduces the size of xdr_reserve_space() from
10 cache lines to 4 on my test system.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xdr.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index b57cf9df4de8..08a85375b311 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -945,8 +945,13 @@ inline void xdr_commit_encode(struct xdr_stream *xdr)
 }
 EXPORT_SYMBOL_GPL(xdr_commit_encode);
 
-static __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
-		size_t nbytes)
+/*
+ * The buffer space to be reserved crosses the boundary between
+ * xdr->buf->head and xdr->buf->pages, or between two pages
+ * in xdr->buf->pages.
+ */
+static noinline __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
+						   size_t nbytes)
 {
 	__be32 *p;
 	int space_left;