linux-kernel - [PATCH v4 24/40] RDMA/rtrs: optimize __rtrs_get_permit() by using find_and_set_bit

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Date: Thu, 20 Jun 2024 10:56:47 -0700
From: Yury Norov <yury.norov@...il.com>
To: linux-kernel@...r.kernel.org,
	"Md. Haris Iqbal" <haris.iqbal@...os.com>,
	Jack Wang <jinpu.wang@...os.com>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Leon Romanovsky <leon@...nel.org>,
	linux-rdma@...r.kernel.org
Cc: Yury Norov <yury.norov@...il.com>,
	Alexey Klimov <alexey.klimov@...aro.org>,
	Bart Van Assche <bvanassche@....org>,
	Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>,
	Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Shtylyov <s.shtylyov@....ru>
Subject: [PATCH v4 24/40] RDMA/rtrs: optimize __rtrs_get_permit() by using find_and_set_bit_lock()

The function opencodes find_and_set_bit_lock() with a while-loop polling
on test_and_set_bit_lock(). Use the dedicated function instead.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 drivers/infiniband/ulp/rtrs/rtrs-clt.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/drivers/infiniband/ulp/rtrs/rtrs-clt.c b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
index 88106cf5ce55..52b7728f6c63 100644
--- a/drivers/infiniband/ulp/rtrs/rtrs-clt.c
+++ b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
@@ -10,6 +10,7 @@
 #undef pr_fmt
 #define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt
 
+#include <linux/find_atomic.h>
 #include <linux/module.h>
 #include <linux/rculist.h>
 #include <linux/random.h>
@@ -72,18 +73,9 @@ __rtrs_get_permit(struct rtrs_clt_sess *clt, enum rtrs_clt_con_type con_type)
 	struct rtrs_permit *permit;
 	int bit;
 
-	/*
-	 * Adapted from null_blk get_tag(). Callers from different cpus may
-	 * grab the same bit, since find_first_zero_bit is not atomic.
-	 * But then the test_and_set_bit_lock will fail for all the
-	 * callers but one, so that they will loop again.
-	 * This way an explicit spinlock is not required.
-	 */
-	do {
-		bit = find_first_zero_bit(clt->permits_map, max_depth);
-		if (bit >= max_depth)
-			return NULL;
-	} while (test_and_set_bit_lock(bit, clt->permits_map));
+	bit = find_and_set_bit_lock(clt->permits_map, max_depth);
+	if (bit >= max_depth)
+		return NULL;
 
 	permit = get_permit(clt, bit);
 	WARN_ON(permit->mem_id != bit);
-- 
2.43.0