netdev - [net-next v4 08/11] page_pool: Add stat tracking empty ring

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Message-Id: <1643933373-6590-9-git-send-email-jdamato@fastly.com>
Date:   Thu,  3 Feb 2022 16:09:30 -0800
From:   Joe Damato <jdamato@...tly.com>
To:     netdev@...r.kernel.org, kuba@...nel.org,
        ilias.apalodimas@...aro.org, davem@...emloft.net, hawk@...nel.org,
        saeed@...nel.org, ttoukan.linux@...il.com, brouer@...hat.com
Cc:     Joe Damato <jdamato@...tly.com>
Subject: [net-next v4 08/11] page_pool: Add stat tracking empty ring

Add a stat tracking when the ptr ring is empty. When this occurs, the cache
could not be refilled and a slow path allocation was forced.

Signed-off-by: Joe Damato <jdamato@...tly.com>
---
 include/net/page_pool.h | 3 +++
 net/core/page_pool.c    | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index 0c4cb49..b243480 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -146,6 +146,9 @@ 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;
 };
 #endif
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index b7d0995..b25ded1 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -136,8 +136,10 @@ 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)) {
+		this_cpu_inc_alloc_stat(pool, 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