netdev - [PATCH RFC bpf-next 36/52] bpf, cpumap: switch to napi_skb_cache_get

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Date:   Tue, 28 Jun 2022 21:47:56 +0200
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Toke Hoiland-Jorgensen <toke@...hat.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        John Fastabend <john.fastabend@...il.com>,
        Yajun Deng <yajun.deng@...ux.dev>,
        Willem de Bruijn <willemb@...gle.com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        xdp-hints@...-project.net
Subject: [PATCH RFC bpf-next 36/52] bpf, cpumap: switch to napi_skb_cache_get_bulk()

Now that cpumap uses GRO, which drops unused skb heads to the NAPI
cache, use napi_skb_cache_get_bulk() to try to reuse cached entries
and lower the MM layer pressure.
In the situation when all 8 skbs from one cpumap batch goes into one
GRO skb (so the rest 7 go into the cache), there will now be only 1
skb to allocate per cycle instead of 8. If there is some other work
happening in between the cycles, even all 8 might be getting
decached each cycle.
This makes the BH-off period per each batch slightly longer --
previously, skb allocation was happening in the process context.

Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
---
 kernel/bpf/cpumap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 145f49de0931..1bb3ae570e6c 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -365,7 +365,6 @@ static int cpu_map_kthread_run(void *data)
 	while (!kthread_should_stop() || !__ptr_ring_empty(rcpu->queue)) {
 		struct xdp_cpumap_stats stats = {}; /* zero stats */
 		unsigned int kmem_alloc_drops = 0, sched = 0;
-		gfp_t gfp = __GFP_ZERO | GFP_ATOMIC;
 		int i, n, m, nframes, xdp_n;
 		void *frames[CPUMAP_BATCH];
 		void *skbs[CPUMAP_BATCH];
@@ -416,8 +415,10 @@ static int cpu_map_kthread_run(void *data)
 
 		/* Support running another XDP prog on this CPU */
 		nframes = cpu_map_bpf_prog_run(rcpu, frames, xdp_n, &stats, &list);
+		local_bh_disable();
+
 		if (nframes) {
-			m = kmem_cache_alloc_bulk(skbuff_head_cache, gfp, nframes, skbs);
+			m = napi_skb_cache_get_bulk(skbs, nframes);
 			if (unlikely(m == 0)) {
 				for (i = 0; i < nframes; i++)
 					skbs[i] = NULL; /* effect: xdp_return_frame */
@@ -425,7 +426,6 @@ static int cpu_map_kthread_run(void *data)
 			}
 		}
 
-		local_bh_disable();
 		for (i = 0; i < nframes; i++) {
 			struct xdp_frame *xdpf = frames[i];
 			struct sk_buff *skb = skbs[i];
-- 
2.36.1