Re: [dpdk-dev] [PATCH v3] ethdev: fix ethdev data alignment

[Matan Azrad <matan@mellanox.com>]

Hi Jerin

From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> 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")

I don't think you need the add the 5b7ba31148a8 fix line.
Maybe think about it in the next way:
Is your fix can stay as a same fix before the port ownership feature addition?
If yes, You are not fixing it.

I think that the port ownership just exposed the issue, did not initiated it.

> Cc: stable@dpdk.org
> 
> Cc: Matan Azrad <matan@mellanox.com>
> Cc: Thomas Monjalon <thomas@monjalon.net>
> Cc: Konstantin Ananyev <konstantin.ananyev@intel.com>
> 
> Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
> ---
> 
> v3:
> - added more history/data in the git log
> - added stable@dpdk.org in Cc
> 
> v2:
>  - Change the git comments based on Matan's feedback
> https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdpd
> k.org%2Fdev%2Fpatchwork%2Fpatch%2F35104%2F&data=02%7C01%7Cmata
> n%40mellanox.com%7Cd491698ead5f48626c1408d5721a8331%7C8c5c71989d
> be4cf9a2099e499881116c%7C0%7C0%7C636540380570748030&sdata=if8cCrk3
> U0XqWp8NE%2BEP1BjuPHX95HHN0f1yjk6krV0%3D&reserved=0
> 
> ---
>  lib/librte_ether/rte_ethdev_core.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/librte_ether/rte_ethdev_core.h
> b/lib/librte_ether/rte_ethdev_core.h
> index 315b31723..e5681e466 100644
> --- a/lib/librte_ether/rte_ethdev_core.h
> +++ b/lib/librte_ether/rte_ethdev_core.h
> @@ -601,7 +601,7 @@ struct rte_eth_dev_data {
>  	struct rte_vlan_filter_conf vlan_filter_conf;
>  	/**< VLAN filter configuration. */
>  	struct rte_eth_dev_owner owner; /**< The port owner. */ -};
> +} __rte_cache_aligned;
> 
>  /**
>   * @internal
> --
> 2.16.1