-----Original Message----- > Date: Mon, 12 Feb 2018 14:02:17 +0000 > From: Matan Azrad <ma...@mellanox.com> > To: Jerin Jacob <jerin.ja...@caviumnetworks.com> > CC: "dev@dpdk.org" <dev@dpdk.org>, "ferruh.yi...@intel.com" > <ferruh.yi...@intel.com>, "sta...@dpdk.org" <sta...@dpdk.org>, Thomas > Monjalon <tho...@monjalon.net>, Konstantin Ananyev > <konstantin.anan...@intel.com>, Pavan Nikhilesh > <pbhagavat...@caviumnetworks.com> > Subject: RE: [dpdk-dev] [PATCH v3] ethdev: fix ethdev data alignment > > > > From: Jerin Jacob, Sent: Monday, February 12, 2018 3:51 PM > > -----Original Message----- > > > Date: Mon, 12 Feb 2018 13:44:54 +0000 > > > From: Matan Azrad <ma...@mellanox.com> > > > To: Jerin Jacob <jerin.ja...@caviumnetworks.com>, "dev@dpdk.org" > > > <dev@dpdk.org> > > > CC: "ferruh.yi...@intel.com" <ferruh.yi...@intel.com>, "sta...@dpdk.org" > > > <sta...@dpdk.org>, Thomas Monjalon <tho...@monjalon.net>, > > Konstantin > > > Ananyev <konstantin.anan...@intel.com>, Pavan Nikhilesh > > > <pbhagavat...@caviumnetworks.com> > > > Subject: RE: [dpdk-dev] [PATCH v3] ethdev: fix ethdev data alignment > > > > > > Hi Jerin > > > > > > From: Jerin Jacob [mailto:jerin.ja...@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 don't think so. 5b7ba31148a8 breaking the first port alignment case(as > > mentioned in the commit log clearly). > > First port alignment was correct prior to 5b7ba31148a8 change set > > > > Do you agree? > > No. > The root cause of the issue this fix is fixing, is that the structure is not > aligned, it is not relevant to port ownership. > The port ownership just exposes it.
My point is simple. First port alignment was correct prior to 5b7ba31148a8 change set. it is broken from there. It is minor thing. I let, ethdev maintainer to decide what to added in Fixes on apply.
