page_pool: place frag_* fields in one cacheline

On x86_64, frag_* fields of struct page_pool are scattered across two
cachelines despite the summary size of 24 bytes. All three fields are
used in pretty much the same places, but the last field, ::frag_users,
is pushed out to the next CL, provoking unwanted false-sharing on
hotpath (frags allocation code).
There are some holes and cold members to move around. Move frag_* one
block up, placing them right after &page_pool_params perfectly at the
beginning of CL2. This doesn't do any meaningful to the second block, as
those are some destroy-path cold structures, and doesn't do anything to
::alloc_stats, which still starts at 200-byte offset, 8 bytes after CL3
(still fitting into 1 cacheline).
On my setup, this yields 1-2% of Mpps when using PP frags actively.
When it comes to 32-bit architectures with 32-byte CL: &page_pool_params
plus ::pad is 44 bytes, the block taken care of is 16 bytes within one
CL, so there should be at least no regressions from the actual change.
::pages_state_hold_cnt is not related directly to that triple, but is
paired currently with ::frags_offset and decoupling them would mean
either two 4-byte holes or more invasive layout changes.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Link: https://lore.kernel.org/r/20230804180529.2483231-4-aleksander.lobakin@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
index fcb8465..887e794 100644 (file)
--- a/include/net/page_pool/types.h
+++ b/include/net/page_pool/types.h
@@ -123,16 +123,16 @@ struct page_pool_stats {
 struct page_pool {
        struct page_pool_params p;
 
+       long frag_users;
+       struct page *frag_page;
+       unsigned int frag_offset;
+       u32 pages_state_hold_cnt;
+
        struct delayed_work release_dw;
        void (*disconnect)(void *pool);
        unsigned long defer_start;
        unsigned long defer_warn;
 
-       u32 pages_state_hold_cnt;
-       unsigned int frag_offset;
-       struct page *frag_page;
-       long frag_users;
-
 #ifdef CONFIG_PAGE_POOL_STATS
        /* these stats are incremented while in softirq context */
        struct page_pool_alloc_stats alloc_stats;