-----Original Message----- Hi Konstantin,
> > > -----Original Message----- > > From: Jerin Jacob [mailto:jerin.ja...@caviumnetworks.com] > > Sent: Thursday, April 5, 2018 9:02 AM > > To: Ananyev, Konstantin <konstantin.anan...@intel.com> > > Cc: Olivier Matz <olivier.m...@6wind.com>; dev@dpdk.org; Richardson, Bruce > > <bruce.richard...@intel.com> > > Subject: Re: [dpdk-dev] [PATCH] ring: relax alignment constraint on ring > > structure > > > > -----Original Message----- > > > Date: Wed, 4 Apr 2018 23:38:41 +0000 > > > From: "Ananyev, Konstantin" <konstantin.anan...@intel.com> > > > To: Jerin Jacob <jerin.ja...@caviumnetworks.com>, Olivier Matz > > > <olivier.m...@6wind.com> > > > CC: "dev@dpdk.org" <dev@dpdk.org>, "Richardson, Bruce" > > > <bruce.richard...@intel.com> > > > Subject: RE: [dpdk-dev] [PATCH] ring: relax alignment constraint on ring > > > structure > > > > > > Hi lads, > > > > > > > -----Original Message----- > > > > From: Jerin Jacob [mailto:jerin.ja...@caviumnetworks.com] > > > > Sent: Tuesday, April 3, 2018 5:43 PM > > > > To: Olivier Matz <olivier.m...@6wind.com> > > > > Cc: dev@dpdk.org; Ananyev, Konstantin <konstantin.anan...@intel.com>; > > > > Richardson, Bruce <bruce.richard...@intel.com> > > > > Subject: Re: [dpdk-dev] [PATCH] ring: relax alignment constraint on > > > > ring structure > > > > > > > > -----Original Message----- > > > > > Date: Tue, 3 Apr 2018 17:56:01 +0200 > > > > > From: Olivier Matz <olivier.m...@6wind.com> > > > > > To: Jerin Jacob <jerin.ja...@caviumnetworks.com> > > > > > CC: dev@dpdk.org, konstantin.anan...@intel.com, > > > > > bruce.richard...@intel.com > > > > > Subject: Re: [dpdk-dev] [PATCH] ring: relax alignment constraint on > > > > > ring > > > > > structure > > > > > User-Agent: NeoMutt/20170113 (1.7.2) > > > > > > > > > > On Tue, Apr 03, 2018 at 09:07:04PM +0530, Jerin Jacob wrote: > > > > > > -----Original Message----- > > > > > > > Date: Tue, 3 Apr 2018 17:25:17 +0200 > > > > > > > From: Olivier Matz <olivier.m...@6wind.com> > > > > > > > To: Jerin Jacob <jerin.ja...@caviumnetworks.com> > > > > > > > CC: dev@dpdk.org, konstantin.anan...@intel.com, > > > > > > > bruce.richard...@intel.com > > > > > > > Subject: Re: [dpdk-dev] [PATCH] ring: relax alignment constraint > > > > > > > on ring > > > > > > > structure > > > > > > > User-Agent: NeoMutt/20170113 (1.7.2) > > > > > > > > > > > > > > On Tue, Apr 03, 2018 at 08:37:23PM +0530, Jerin Jacob wrote: > > > > > > > > -----Original Message----- > > > > > > > > > Date: Tue, 3 Apr 2018 15:26:44 +0200 > > > > > > > > > From: Olivier Matz <olivier.m...@6wind.com> > > > > > > > > > To: dev@dpdk.org > > > > > > > > > Subject: [dpdk-dev] [PATCH] ring: relax alignment constraint > > > > > > > > > on ring > > > > > > > > > structure > > > > > > > > > X-Mailer: git-send-email 2.11.0 > > > > > > > > > > > > > > > > > > The initial objective of > > > > > > > > > commit d9f0d3a1ffd4 ("ring: remove split cacheline build > > > > > > > > > setting") > > > > > > > > > was to add an empty cache line betwee, the producer and > > > > > > > > > consumer > > > > > > > > > data (on platform with cache line size = 64B), preventing from > > > > > > > > > having them on adjacent cache lines. > > > > > > > > > > > > > > > > > > Following discussion on the mailing list, it appears that this > > > > > > > > > also imposes an alignment constraint that is not required. > > > > > > > > > > > > > > > > > > This patch removes the extra alignment constraint and adds the > > > > > > > > > empty cache lines using padding fields in the structure. The > > > > > > > > > size of rte_ring structure and the offset of the fields remain > > > > > > > > > the same on platforms with cache line size = 64B: > > > > > > > > > > > > > > > > > > rte_ring = 384 > > > > > > > > > rte_ring.name = 0 > > > > > > > > > rte_ring.flags = 32 > > > > > > > > > rte_ring.memzone = 40 > > > > > > > > > rte_ring.size = 48 > > > > > > > > > rte_ring.mask = 52 > > > > > > > > > rte_ring.prod = 128 > > > > > > > > > rte_ring.cons = 256 > > > > > > > > > > > > > > > > > > But it has an impact on platform where cache line size is > > > > > > > > > 128B: > > > > > > > > > > > > > > > > > > rte_ring = 384 -> 768 > > > > > > > > > rte_ring.name = 0 > > > > > > > > > rte_ring.flags = 32 > > > > > > > > > rte_ring.memzone = 40 > > > > > > > > > rte_ring.size = 48 > > > > > > > > > rte_ring.mask = 52 > > > > > > > > > rte_ring.prod = 128 -> 256 > > > > > > > > > rte_ring.cons = 256 -> 512 > > > > > > > > > > > > > > > > Are we leaving TWO cacheline to make sure, HW prefetch don't > > > > > > > > load > > > > > > > > the adjust cacheline(consumer)? > > > > > > > > > > > > > > > > If so, Will it have impact on those machine where it is 128B > > > > > > > > Cache line > > > > > > > > and the HW prefetcher is not loading the next caching > > > > > > > > explicitly. Right? > > > > > > > > > > > > > > The impact on machines that have a 128B cache line is that an > > > > > > > unused > > > > > > > cache line will be added between the producer and consumer data. I > > > > > > > expect that the impact is positive in case there is a hw > > > > > > > prefetcher, and > > > > > > > null in case there is no such prefetcher. > > > > > > > > > > > > It is not NULL, Right? You are loosing 256B for each ring. > > > > > > > > > > Is it really that important? > > > > > > > > Pipeline or eventdev SW cases there could more rings in the system. > > > > I don't see any downside of having config option which is enabled > > > > default. > > > > > > > > In my view, such config options are good, as in embedded usecases, > > > > customers > > > > can really fine tune the target for the need. In server usecases, let > > > > the default > > > > of option be enabled, no harm. > > > > > > But that would mean we have to maintain two layouts for the rte_ring > > > structure. > > > > Is there any downside of having two configurable layout? meaning, we are not > > transferring rte_ring structure over network etc(ie no interoperability > > issue). Does it really matter? May I am missing something here. > > My concern about potential compatibility problems we are introducing - > library build with 'y', while app wit 'n', or visa-versa. Got it. > I wonder are there really a lot of users who would be interested in such > savings? > Could it happen that this new option would sit here unused and untested? OK. Fair enough. I have no objections for Olivier patch. As a suggestion, may be we can move "char name[RTE_MEMZONE_NAMESIZE]" in the struct rte_ring in place of " empty cacheline" to save 32B. No strong option though. > Konstantin > > > > > I was thinking like this: > > > > in config/common_base: > > CONFIG_RTE_EAL_HAS_HW_PREFETCH=y > > > > #ifdef RTE_EAL_HAS_HW_PREFETCH > > #define EMPTY_CACHE_LINE char pad0 __rte_cache_aligned > > #else > > #define EMPTY_CACHE_LINE > > #endif > > > > struct rte_ring_headtail { > > .. > > .. > > char pad0 __rte_cache_aligned; /**< empty cache line */ > > struct rte_ring_headtail prod __rte_cache_aligned; > > EMPTY_CACHE_LINE > > struct rte_ring_headtail cons __rte_cache_aligned; > > EMPTY_CACHE_LINE > > } >
