netdev - [PATCH v2 net-next 07/10] s390/qeth: indicate contiguous TX buffer elements

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Date:   Wed,  6 May 2020 10:09:46 +0200
From:   Julian Wiedmann <jwi@...ux.ibm.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Ursula Braun <ubraun@...ux.ibm.com>,
        Julian Wiedmann <jwi@...ux.ibm.com>
Subject: [PATCH v2 net-next 07/10] s390/qeth: indicate contiguous TX buffer elements

The TX path usually maps the full content of a page into a buffer
element. But there's specific skb layouts (ie. linearized TSO skbs)
where the HW header (1) requires a separate buffer element, and (2) is
page-contiguous with the packet data that's mapped into the next buffer
element.
Flag such buffer elements accordingly, so that HW can optimize its data
access for them.

Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>
---
 drivers/s390/net/qeth_core_main.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index 9c9a6edb5384..4d1d053eebb7 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -4110,8 +4110,16 @@ static unsigned int qeth_fill_buffer(struct qeth_qdio_out_buffer *buf,
 		buffer->element[element].addr = virt_to_phys(hdr);
 		buffer->element[element].length = hd_len;
 		buffer->element[element].eflags = SBAL_EFLAGS_FIRST_FRAG;
-		/* remember to free cache-allocated HW header: */
-		buf->is_header[element] = ((void *)hdr != skb->data);
+
+		/* HW header is allocated from cache: */
+		if ((void *)hdr != skb->data)
+			buf->is_header[element] = 1;
+		/* HW header was pushed and is contiguous with linear part: */
+		else if (length > 0 && !PAGE_ALIGNED(data) &&
+			 (data == (char *)hdr + hd_len))
+			buffer->element[element].eflags |=
+				SBAL_EFLAGS_CONTIGUOUS;
+
 		element++;
 	}
 
-- 
2.17.1