netdev - [PATCH v2 net-next 2/6] net: tso: double TSO_HEADER

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Message-Id: <20200618035326.39686-3-edumazet@google.com>
Date:   Wed, 17 Jun 2020 20:53:22 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Sunil Goutham <sgoutham@...vell.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>
Subject: [PATCH v2 net-next 2/6] net: tso: double TSO_HEADER_SIZE value

Transport header size could be 60 bytes, and network header
size can also be 60 bytes. Add the Ethernet header and we
are above 128 bytes.

Since drivers using net/core/tso.c usually allocates
one DMA coherent piece of memory per TX queue, this patch
might cause issues if a driver was using too many slots.

For 1024 slots, we would need 256 KB of physically
contiguous memory instead of 128 KB.

Alternative fix would be to add checks in the fast path,
but this involves more work in all drivers using net/core/tso.c.

Fixes: f9cbe9a556af ("net: define the TSO header size in net/tso.h")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Antoine Tenart <antoine.tenart@...tlin.com>
---
 include/net/tso.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/tso.h b/include/net/tso.h
index 7e166a5703497fadf4662acc474f827b2754da78..c33dd00c161f7a6aa65f586b0ceede46af2e8730 100644
--- a/include/net/tso.h
+++ b/include/net/tso.h
@@ -4,7 +4,7 @@
 
 #include <net/ip.h>
 
-#define TSO_HEADER_SIZE		128
+#define TSO_HEADER_SIZE		256
 
 struct tso_t {
 	int next_frag_idx;
-- 
2.27.0.290.gba653c62da-goog