netdev - [PATCH v2 net-next 23/26] igc: bail out early on XSK xmit if no descs are available

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Date:   Tue, 23 Nov 2021 17:39:52 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Shay Agroskin <shayagr@...zon.com>,
        Arthur Kiyanovski <akiyano@...zon.com>,
        David Arinzon <darinzon@...zon.com>,
        Noam Dagan <ndagan@...zon.com>,
        Saeed Bishara <saeedb@...zon.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Yajun Deng <yajun.deng@...ux.dev>,
        Sergey Ryazanov <ryazanov.s.a@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Cong Wang <cong.wang@...edance.com>, netdev@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH v2 net-next 23/26] igc: bail out early on XSK xmit if no descs are available

There's no need to fetch an XSK pool desc in case our ring is full,
we can rather quit under unlikely branch.
Can't skip taking a lock here unfortunately since igc_desc_unused()
assumes we call it being locked.
This was designed to track xsk_tx::full counter, but won't hurt
either way.

Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 8e448288ee26..7d0c540d6b76 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -2604,6 +2604,8 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
 	__netif_tx_lock(nq, cpu);

 	budget = igc_desc_unused(ring);
+	if (unlikely(!budget))
+		goto out_unlock;

 	while (xsk_tx_peek_desc(pool, &xdp_desc) && budget--) {
 		u32 cmd_type, olinfo_status;
@@ -2644,6 +2646,7 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
 		xsk_tx_release(pool);
 	}

+out_unlock:
 	__netif_tx_unlock(nq);
 }

--
2.33.1