[PATCH net-next] page_pool: let the compiler optimize and inline core functions

From: Alexander Lobakin
Date: Mon Mar 22 2021 - 14:31:39 EST

As per disscussion in Page Pool bulk allocator thread [0],
there are two functions in Page Pool core code that are marked as
'noinline'. The reason for this is not so clear, and even if it
was made to reduce hotpath overhead, in fact it only makes things
As both of these functions as being called only once through the
code, they could be inlined/folded into the non-static entry point.
However, 'noinline' marks effectively prevent from doing that and
induce totally unneeded fragmentation (baseline -> after removal):

add/remove: 0/3 grow/shrink: 1/0 up/down: 1024/-1096 (-72)
Function old new delta
page_pool_alloc_pages 100 1124 +1024
page_pool_dma_map 164 - -164
page_pool_refill_alloc_cache 332 - -332
__page_pool_alloc_pages_slow 600 - -600

(taken from Mel's branch, hence factored-out page_pool_dma_map())

1124 is a normal hotpath frame size, but these jumps between tiny
page_pool_alloc_pages(), page_pool_refill_alloc_cache() and
__page_pool_alloc_pages_slow() are really redundant and harmful
for performance.

This simple removal of 'noinline' keywords bumps the throughput
on XDP_PASS + napi_build_skb() + napi_gro_receive() on 25+ Mbps
for 1G embedded NIC.

[0] https://lore.kernel.org/netdev/20210317222506.1266004-1-alobakin@xxxxx

Signed-off-by: Alexander Lobakin <alobakin@xxxxx>
net/core/page_pool.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index ad8b0707af04..589e4df6ef2b 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -102,7 +102,6 @@ EXPORT_SYMBOL(page_pool_create);

static void page_pool_return_page(struct page_pool *pool, struct page *page);

static struct page *page_pool_refill_alloc_cache(struct page_pool *pool)
struct ptr_ring *r = &pool->ring;
@@ -181,7 +180,6 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,

/* slow path */
static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
gfp_t _gfp)