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

[Thomas Monjalon <thomas@monjalon.net>]

12/02/2018 14:13, Jerin Jacob:
> 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")
> 
> 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>
> ---
Acked-by: Thomas Monjalon <thomas@monjalon.net>

Applied, thanks