netdev - [PATCH bpf-next] xsk: bump xsk_queue::queue_empty_descs in xp_can

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Message-Id: <20240904162808.249160-1-maciej.fijalkowski@intel.com>
Date: Wed,  4 Sep 2024 18:28:08 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: bpf@...r.kernel.org,
	ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org
Cc: netdev@...r.kernel.org,
	magnus.karlsson@...el.com,
	bjorn@...nel.org,
	maciej.fijalkowski@...el.com
Subject: [PATCH bpf-next] xsk: bump xsk_queue::queue_empty_descs in xp_can_alloc()

We have STAT_FILL_EMPTY test case in xskxceiver that tries to process
traffic with fill queue being empty which currently fails for zero copy
ice driver after it started to use xsk_buff_can_alloc() API. That is
because xsk_queue::queue_empty_descs is currently only increased from
alloc APIs and right now if driver sees that xsk_buff_pool will be
unable to provide the requested count of buffers, it bails out early,
skipping calls to xsk_buff_alloc{_batch}().

Mentioned statistic should be handled in xsk_buff_can_alloc() from the
very beginning, so let's add this logic now. Do it by open coding
xskq_cons_has_entries() and bumping queue_empty_descs in the middle when
fill queue currently has no entries.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
---
 net/xdp/xsk_buff_pool.c | 11 ++++++++++-
 net/xdp/xsk_queue.h     |  5 -----
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
index c0e0204b9630..29afa880ffa0 100644
--- a/net/xdp/xsk_buff_pool.c
+++ b/net/xdp/xsk_buff_pool.c
@@ -656,9 +656,18 @@ EXPORT_SYMBOL(xp_alloc_batch);
 
 bool xp_can_alloc(struct xsk_buff_pool *pool, u32 count)
 {
+	u32 req_count, avail_count;
+
 	if (pool->free_list_cnt >= count)
 		return true;
-	return xskq_cons_has_entries(pool->fq, count - pool->free_list_cnt);
+	req_count = count - pool->free_list_cnt;
+
+	avail_count = xskq_cons_nb_entries(pool->fq, req_count);
+
+	if (!avail_count)
+		pool->fq->queue_empty_descs++;
+
+	return avail_count >= req_count;
 }
 EXPORT_SYMBOL(xp_can_alloc);
 
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 6f2d1621c992..406b20dfee8d 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -306,11 +306,6 @@ static inline u32 xskq_cons_nb_entries(struct xsk_queue *q, u32 max)
 	return entries >= max ? max : entries;
 }
 
-static inline bool xskq_cons_has_entries(struct xsk_queue *q, u32 cnt)
-{
-	return xskq_cons_nb_entries(q, cnt) >= cnt;
-}
-
 static inline bool xskq_cons_peek_addr_unchecked(struct xsk_queue *q, u64 *addr)
 {
 	if (q->cached_prod == q->cached_cons)
-- 
2.34.1