[dpdk-stable] patch 'ethdev: fix data alignment' has been queued to LTS release 16.11.5

[Luca Boccassi]

Hi,

FYI, your patch has been queued to LTS release 16.11.5

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 02/17/18. So please
shout if anyone has objections.

Thanks.

Luca Boccassi

---
>From 648370d23204f13c3ec35baf68ed4f9e539a5bfd Mon Sep 17 00:00:00 2001
From: Jerin Jacob <jerin.jacob at caviumnetworks.com>
Date: Mon, 12 Feb 2018 18:43:43 +0530
Subject: [PATCH] ethdev: fix data alignment

[ upstream commit 740cecb24f52a945c0d40d6073ff0b2acc5c0616 ]

The struct rte_eth_dev_data is used in ethdev fastpath routines
and it not aligned to cache line size. This patch fixes the ethdev
data alignment.

The alignment was broken from the "first public release" changeset
where ethdev data address was aligned only to the first port.
Remaining ports alignment was defined by the size of the struct
(rte_eth_dev_data). This scheme is not guaranteed to be cache line
aligned all the time.

"ethdev: add port ownership" change set introduced a
rte_eth_dev_shared_data container for port ownership change,
This resulted in rte_eth_dev->data memory for the first port also
as cache unaligned.

Added a compiler alignment attribute to make sure
rte_eth_dev->data always cache aligned so that CPU/compiler
1) Avoid sharing the element with another cache line
2) Can load/store the elements in struct rte_eth_dev_data as
naturally aligned.

Some platform like thunderX could see performance regression of 1%
at "ethdev: add port ownership" change set with
1 port/1 queue l3fwd application and this patch fixes that regression.

example command:
sudo ./examples/l3fwd/build/l3fwd -c 0xff00 -- -p 0x1 --config="(0,0,9)"

Fixes: af75078fece3 ("first public release")
Fixes: 5b7ba31148a8 ("ethdev: add port ownership")

Signed-off-by: Jerin Jacob <jerin.jacob at caviumnetworks.com>
Signed-off-by: Pavan Nikhilesh <pbhagavatula at caviumnetworks.com>
Acked-by: Thomas Monjalon <thomas at monjalon.net>
---
 lib/librte_ether/rte_ethdev.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
index 13a7c8a86..dc6d0cc91 100644
--- a/lib/librte_ether/rte_ethdev.h
+++ b/lib/librte_ether/rte_ethdev.h
@@ -1694,7 +1694,7 @@ struct rte_eth_dev_data {
 	enum rte_kernel_driver kdrv;    /**< Kernel driver passthrough */
 	int numa_node;  /**< NUMA node connection */
 	const char *drv_name;   /**< Driver name */
-};
+} __rte_cache_aligned;
 
 /** Device supports hotplug detach */
 #define RTE_ETH_DEV_DETACHABLE   0x0001
-- 
2.14.2