xsk: align &xdp_buff_xsk harder

After the series "XSk buff on a diet" by Maciej, the greatest pow-2
which &xdp_buff_xsk can be divided got reduced from 16 to 8 on x86_64.
Also, sizeof(xdp_buff_xsk) now is 120 bytes, which, taking the previous
sentence into account, leads to that it leaves 8 bytes at the end of
cacheline, which means an array of buffs will have its elements
messed between the cachelines chaotically.
Use __aligned_largest for this struct. This alignment is usually 16
bytes, which makes it fill two full cachelines and align an array
nicely. ___cacheline_aligned may be excessive here, especially on
arches with 128-256 byte CLs, as well as 32-bit arches (76 -> 96
bytes on MIPS32R2), while not doing better than _largest.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://patch.msgid.link/20241203173733.3181246-2-aleksander.lobakin@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
index bb03cee716b316f22c3181240a1823a4477f7f6b..7637799b6c19294e2d9ee912e7c14d9992dc9050 100644 (file)
--- a/include/net/xsk_buff_pool.h
+++ b/include/net/xsk_buff_pool.h
@@ -29,7 +29,7 @@ struct xdp_buff_xsk {
        dma_addr_t frame_dma;
        struct xsk_buff_pool *pool;
        struct list_head list_node;
-};
+} __aligned_largest;
 
 #define XSK_CHECK_PRIV_TYPE(t) BUILD_BUG_ON(sizeof(t) > offsetofend(struct xdp_buff_xsk, cb))
 #define XSK_TX_COMPL_FITS(t) BUILD_BUG_ON(sizeof(struct xsk_tx_metadata_compl) > sizeof(t))