netdev - [PATCH net-next v2] tun: replace get_cpu_ptr with this_cpu

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Message-Id: <20181211024307.7156-1-bhole_prashant_q7@lab.ntt.co.jp>
Date:   Tue, 11 Dec 2018 11:43:07 +0900
From:   Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>,
        Jason Wang <jasowang@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
        Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Subject: [PATCH net-next v2] tun: replace get_cpu_ptr with this_cpu_ptr when bh disabled

tun_xdp_one() runs with local bh disabled. So there is no need to
disable preemption by calling get_cpu_ptr while updating stats. This
patch replaces the use of get_cpu_ptr() with this_cpu_ptr() as a
micro-optimization. Also removes related put_cpu_ptr call.

Acked-by: Jason Wang <jasowang@...hat.com>
Signed-off-by: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
---
v1 -> v2: Added comment to explain why this change is safe

 drivers/net/tun.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 6760b86547df..cb90859d0433 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2494,12 +2494,14 @@ static int tun_xdp_one(struct tun_struct *tun,
 	skb_record_rx_queue(skb, tfile->queue_index);
 	netif_receive_skb(skb);
 
-	stats = get_cpu_ptr(tun->pcpu_stats);
+	/* No need for get_cpu_ptr() here since this function is
+	 * always called with bh disabled
+	 */
+	stats = this_cpu_ptr(tun->pcpu_stats);
 	u64_stats_update_begin(&stats->syncp);
 	stats->rx_packets++;
 	stats->rx_bytes += skb->len;
 	u64_stats_update_end(&stats->syncp);
-	put_cpu_ptr(stats);
 
 	if (rxhash)
 		tun_flow_update(tun, rxhash, tfile);
-- 
2.17.2