From 4a36d0180c452c3482792e0ff14e2bcf536a9284 Mon Sep 17 00:00:00 2001 From: Alexander Lobakin Date: Fri, 4 Aug 2023 20:05:29 +0200 Subject: [PATCH] net: skbuff: always try to recycle PP pages directly when in softirq Commit 8c48eea3adf3 ("page_pool: allow caching from safely localized NAPI") allowed direct recycling of skb pages to their PP for some cases, but unfortunately missed a couple of other majors. For example, %XDP_DROP in skb mode. The netstack just calls kfree_skb(), which unconditionally passes `false` as @napi_safe. Thus, all pages go through ptr_ring and locks, although most of time we're actually inside the NAPI polling this PP is linked with, so that it would be perfectly safe to recycle pages directly. Let's address such. If @napi_safe is true, we're fine, don't change anything for this path. But if it's false, check whether we are in the softirq context. It will most likely be so and then if ->list_owner is our current CPU, we're good to use direct recycling, even though @napi_safe is false -- concurrent access is excluded. in_softirq() protection is needed mostly due to we can hit this place in the process context (not the hardirq though). For the mentioned xdp-drop-skb-mode case, the improvement I got is 3-4% in Mpps. As for page_pool stats, recycle_ring is now 0 and alloc_slow counter doesn't change most of time, which means the MM layer is not even called to allocate any new pages. Suggested-by: Jakub Kicinski # in_softirq() Signed-off-by: Alexander Lobakin Reviewed-by: Alexander Duyck Link: https://lore.kernel.org/r/20230804180529.2483231-7-aleksander.lobakin@intel.com Signed-off-by: Jakub Kicinski --- net/core/skbuff.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 85f82a6..33fdf04 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -902,8 +902,10 @@ bool napi_pp_put_page(struct page *page, bool napi_safe) /* Allow direct recycle if we have reasons to believe that we are * in the same context as the consumer would run, so there's * no possible race. + * __page_pool_put_page() makes sure we're not in hardirq context + * and interrupts are enabled prior to accessing the cache. */ - if (napi_safe) { + if (napi_safe || in_softirq()) { const struct napi_struct *napi = READ_ONCE(pp->p.napi); allow_direct = napi && -- 2.7.4