netdev - [PATCH net-next 4/6] net: page_pool: Add stat tracking empty ring

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Message-Id: <1643237300-44904-5-git-send-email-jdamato@fastly.com>
Date:   Wed, 26 Jan 2022 14:48:18 -0800
From:   Joe Damato <jdamato@...tly.com>
To:     netdev@...r.kernel.org
Cc:     kuba@...nel.org, davem@...emloft.net, ilias.apalodimas@...aro.org,
        hawk@...nel.org, Joe Damato <jdamato@...tly.com>
Subject: [PATCH net-next 4/6] net: page_pool: Add stat tracking empty ring

Add a stat tracking when the ptr ring is empty. A static inline wrapper
function is exposed to access this stat.

Signed-off-by: Joe Damato <jdamato@...tly.com>
---
 include/net/page_pool.h | 15 +++++++++++++++
 net/core/page_pool.c    |  4 +++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index b024197..92edf8e 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -84,6 +84,10 @@ struct page_pool_stats {
 		u64 fast; /* fast path allocations */
 		u64 slow; /* slow-path order-0 allocations */
 		u64 slow_high_order; /* slow-path high order allocations */
+		u64 empty; /* failed refills due to empty ptr ring, forcing
+			    * slow path allocation
+			    */
+
 	} alloc;
 };
 
@@ -212,6 +216,12 @@ static inline u64 page_pool_stats_get_slow_high_order(struct page_pool *pool)
 {
 	return pool->ps.alloc.slow_high_order;
 }
+
+static inline u64 page_pool_stats_get_empty(struct page_pool *pool)
+{
+	return pool->ps.alloc.empty;
+}
+
 #else
 static inline void page_pool_destroy(struct page_pool *pool)
 {
@@ -246,6 +256,11 @@ static inline u64 page_pool_stats_get_slow_high_order(struct page_pool *pool)
 {
 	return 0;
 }
+
+static inline u64 page_pool_stats_get_empty(struct page_pool *pool)
+{
+	return 0;
+}
 #endif
 
 void page_pool_put_page(struct page_pool *pool, struct page *page,
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 3a4b912..0de9d58 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -117,8 +117,10 @@ static struct page *page_pool_refill_alloc_cache(struct page_pool *pool)
 	int pref_nid; /* preferred NUMA node */
 
 	/* Quicker fallback, avoid locks when ring is empty */
-	if (__ptr_ring_empty(r))
+	if (__ptr_ring_empty(r)) {
+		pool->ps.alloc.empty++;
 		return NULL;
+	}
 
 	/* Softirq guarantee CPU and thus NUMA node is stable. This,
 	 * assumes CPU refilling driver RX-ring will also run RX-NAPI.
-- 
2.7.4