[PATCH RFC net-next v2 6/7] net: skbuff: avoid accessing page_pool if !napi_safe when returning page
From: Alexander Lobakin <aleksander.lobakin@intel.com>
Date: 2023-07-14 17:11:12
Also in:
lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Currently, pp->p.napi is always read, but the actual variable it gets assigned to is read-only when @napi_safe is true. For the !napi_safe cases, which yet is still a pack, it's an unneeded operation. Moreover, it can lead to premature or even redundant page_pool cacheline access. For example, when page_pool_is_last_frag() returns false (with the recent frag improvements). Thus, read it only when @napi_safe is true. This also allows moving @napi inside the condition block itself. Constify it while we are here, because why not. Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com> --- net/core/skbuff.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4de280c454e4..fc1470aab5cf 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c@@ -881,9 +881,8 @@ static void skb_clone_fraglist(struct sk_buff *skb) bool page_pool_return_skb_page(struct page *page, bool napi_safe) { - struct napi_struct *napi; + bool allow_direct = false; struct page_pool *pp; - bool allow_direct; page = compound_head(page);
@@ -903,9 +902,12 @@ bool page_pool_return_skb_page(struct page *page, bool napi_safe) * in the same context as the consumer would run, so there's * no possible race. */ - napi = READ_ONCE(pp->p.napi); - allow_direct = napi_safe && napi && - READ_ONCE(napi->list_owner) == smp_processor_id(); + if (napi_safe) { + const struct napi_struct *napi = READ_ONCE(pp->p.napi); + + allow_direct = napi && + READ_ONCE(napi->list_owner) == smp_processor_id(); + } /* Driver set this to memory recycling info. Reset it on recycle. * This will *not* work for NIC using a split-page memory model.
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2.41.0