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From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	"olivier.matz@6wind.com" <olivier.matz@6wind.com>,
	"sthemmin@microsoft.com" <sthemmin@microsoft.com>,
	"jerinj@marvell.com" <jerinj@marvell.com>,
	"Richardson, Bruce" <bruce.richardson@intel.com>,
	"david.marchand@redhat.com" <david.marchand@redhat.com>,
	"pbhagavatula@marvell.com" <pbhagavatula@marvell.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	Dharmik Thakkar <Dharmik.Thakkar@arm.com>,
	 Ruifeng Wang <Ruifeng.Wang@arm.com>, Gavin Hu <Gavin.Hu@arm.com>,
	nd <nd@arm.com>, nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH v7 02/17] lib/ring: apis to support configurable element size
Date: Wed, 8 Jan 2020 10:05:23 +0000	[thread overview]
Message-ID: <SN6PR11MB2558806861F0DE439863544F9A3E0@SN6PR11MB2558.namprd11.prod.outlook.com> (raw)
In-Reply-To: <AM0PR08MB51380D18DCB22BEF0FA348A8983E0@AM0PR08MB5138.eurprd08.prod.outlook.com>



> <snip>
> > > > > > > > +
> > > > > > > > +static __rte_always_inline void enqueue_elems_128(struct
> > > > > > > > +rte_ring *r, uint32_t prod_head, const void *obj_table,
> > > > > > > > +uint32_t n) { unsigned int i; const uint32_t size =
> > > > > > > > +r->size; uint32_t idx = prod_head & r->mask; __uint128_t
> > > > > > > > +*ring = (__uint128_t *)&r[1]; const __uint128_t *obj =
> > > > > > > > +(const __uint128_t *)obj_table; if (likely(idx + n < size))
> > > > > > > > +{ for (i = 0; i < (n & ~0x1); i += 2, idx += 2) { ring[idx]
> > > > > > > > += obj[i]; ring[idx + 1] = obj[i + 1];
> > > > > > >
> > > > > > >
> > > > > > > AFAIK, that implies 16B aligned obj_table...
> > > > > > > Would it always be the case?
> > > > > > I am not sure from the compiler perspective.
> > > > > > At least on Arm architecture, unaligned access (address that is
> > > > > > accessed is not aligned to the size of the data element being
> > > > > > accessed) will result in faults or require additional cycles.
> > > > > > So, aligning on
> > > > 16B should be fine.
> > > > > Further, I would be changing this to use 'rte_int128_t' as
> > > > > '__uint128_t' is
> > > > not defined on 32b systems.
> > > >
> > > > What I am trying to say: with this code we imply new requirement for
> > > > elems
> > > The only existing use case in DPDK for 16B is the event ring. The event ring
> > already does similar kind of copy (using 'struct rte_event').
> > > So, there is no change in expectations for event ring.
> > > For future code, I think this expectation should be fine since it allows for
> > optimal code.
> > >
> > > > in the ring: when sizeof(elem)==16 it's alignment also has to be at least
> > 16.
> > > > Which from my perspective is not ideal.
> > > Any reasoning?
> >
> > New implicit requirement and inconsistency.
> > Code like that:
> >
> > struct ring_elem {uint64_t a, b;};
> > ....
> > struct ring_elem elem;
> > rte_ring_dequeue_elem(ring, &elem, sizeof(elem));
> >
> > might cause a crash.
> The alignment here is 8B. Assuming that instructions generated will require 16B alignment, it will result in a crash, if configured to generate
> exception.
> But, these instructions are not atomic instructions. At least on aarch64, unaligned access will not result in an exception for non-atomic
> loads/stores. I believe it is the same behavior for x86 as well.

On IA, there are 2 types of 16B load/store instructions: aligned and unaligned.
Aligned are a bit faster, but will cause an exception if used on non 16B aligned address. 
As you using uint128_t * compiler will assume that both src and dst are 16B aligned
and might generate code with aligned instructions.

> 
> > While exactly the same code with:
> >
> > struct ring_elem {uint64_t a, b, c;}; OR struct ring_elem {uint64_t a, b, c, d;};
> >
> > will work ok.
> The alignment for these structures is still 8B. Are you saying this will work because these will be copied using pointer to uint32_t (whose
> alignment is 4B)?

Yes, as we doing uint32_t copies, compiler can't assume the data will be 16B aligned
and will use unaligned instructions.

> 
> >
> > >
> > > > Note that for elem sizes > 16 (24, 32), there is no such constraint.
> > > The rest of them need to be aligned on 4B boundary. However, this should
> > not affect the existing code.
> > > The code for 8B and 16B is kept as is to ensure the performance is not
> > affected for the existing code.
> <snip>


  reply	other threads:[~2020-01-08 10:05 UTC|newest]

Thread overview: 173+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-28 14:46 [dpdk-dev] [PATCH 0/5] lib/ring: templates to support custom " Honnappa Nagarahalli
2019-08-28 14:46 ` [dpdk-dev] [PATCH 1/5] lib/ring: apis to support configurable " Honnappa Nagarahalli
2019-08-28 14:46 ` [dpdk-dev] [PATCH 2/5] lib/ring: add template to support different element sizes Honnappa Nagarahalli
2019-10-01 11:47   ` Ananyev, Konstantin
2019-10-02  4:21     ` Honnappa Nagarahalli
2019-10-02  8:39       ` Ananyev, Konstantin
2019-10-03  3:33         ` Honnappa Nagarahalli
2019-10-03 11:51           ` Ananyev, Konstantin
2019-10-03 12:27             ` Ananyev, Konstantin
2019-10-03 22:49               ` Honnappa Nagarahalli
2019-08-28 14:46 ` [dpdk-dev] [PATCH 3/5] tools/checkpatch: relax constraints on __rte_experimental Honnappa Nagarahalli
2019-08-28 14:46 ` [dpdk-dev] [PATCH 4/5] lib/ring: add ring APIs to support 32b ring elements Honnappa Nagarahalli
2019-08-28 14:46 ` [dpdk-dev] [PATCH 5/5] lib/hash: use ring with 32b element size to save memory Honnappa Nagarahalli
2019-08-28 15:12 ` [dpdk-dev] [PATCH 0/5] lib/ring: templates to support custom element size Jerin Jacob Kollanukkaran
2019-08-28 15:16 ` Pavan Nikhilesh Bhagavatula
2019-08-28 22:59   ` Honnappa Nagarahalli
2019-09-06 19:05 ` [dpdk-dev] [PATCH v2 0/6] " Honnappa Nagarahalli
2019-09-06 19:05   ` [dpdk-dev] [PATCH v2 1/6] lib/ring: apis to support configurable " Honnappa Nagarahalli
2019-09-06 19:05   ` [dpdk-dev] [PATCH v2 2/6] lib/ring: add template to support different element sizes Honnappa Nagarahalli
2019-09-08 19:44     ` Stephen Hemminger
2019-09-09  9:01       ` Bruce Richardson
2019-09-09 22:33         ` Honnappa Nagarahalli
2019-09-06 19:05   ` [dpdk-dev] [PATCH v2 3/6] tools/checkpatch: relax constraints on __rte_experimental Honnappa Nagarahalli
2019-09-06 19:05   ` [dpdk-dev] [PATCH v2 4/6] lib/ring: add ring APIs to support 32b ring elements Honnappa Nagarahalli
2019-09-06 19:05   ` [dpdk-dev] [PATCH v2 5/6] lib/hash: use ring with 32b element size to save memory Honnappa Nagarahalli
2019-09-06 19:05   ` [dpdk-dev] [PATCH v2 6/6] lib/eventdev: use ring templates for event rings Honnappa Nagarahalli
2019-09-09 13:04   ` [dpdk-dev] [PATCH v2 0/6] lib/ring: templates to support custom element size Aaron Conole
2019-10-07 13:49   ` David Marchand
2019-10-08 19:19   ` [dpdk-dev] [PATCH v3 0/2] lib/ring: APIs " Honnappa Nagarahalli
2019-10-08 19:19     ` [dpdk-dev] [PATCH v3 1/2] lib/ring: apis to support configurable " Honnappa Nagarahalli
2019-10-08 19:19     ` [dpdk-dev] [PATCH v3 2/2] test/ring: add test cases for configurable element size ring Honnappa Nagarahalli
2019-10-09  2:47   ` [dpdk-dev] [PATCH v3 0/2] lib/ring: APIs to support custom element size Honnappa Nagarahalli
2019-10-09  2:47     ` [dpdk-dev] [PATCH v4 1/2] lib/ring: apis to support configurable " Honnappa Nagarahalli
2019-10-11 19:21       ` Honnappa Nagarahalli
2019-10-14 19:41         ` Ananyev, Konstantin
2019-10-14 23:56           ` Honnappa Nagarahalli
2019-10-15  9:34             ` Ananyev, Konstantin
2019-10-17  4:46               ` Honnappa Nagarahalli
2019-10-17 11:51                 ` Ananyev, Konstantin
2019-10-17 20:16                   ` Honnappa Nagarahalli
2019-10-17 23:17                     ` David Christensen
2019-10-18  3:18                       ` Honnappa Nagarahalli
2019-10-18  8:04                         ` Jerin Jacob
2019-10-18 16:11                           ` Jerin Jacob
2019-10-21  0:27                             ` Honnappa Nagarahalli
2019-10-18 16:44                           ` Ananyev, Konstantin
2019-10-18 19:03                             ` Honnappa Nagarahalli
2019-10-21  0:36                             ` Honnappa Nagarahalli
2019-10-21  9:04                               ` Ananyev, Konstantin
2019-10-22 15:59                                 ` Ananyev, Konstantin
2019-10-22 17:57                                   ` Ananyev, Konstantin
2019-10-23 18:58                                     ` Honnappa Nagarahalli
2019-10-18 17:23                         ` David Christensen
2019-10-09  2:47     ` [dpdk-dev] [PATCH v4 2/2] test/ring: add test cases for configurable element size ring Honnappa Nagarahalli
2019-10-17 20:08   ` [dpdk-dev] [PATCH v5 0/3] lib/ring: APIs to support custom element size Honnappa Nagarahalli
2019-10-17 20:08     ` [dpdk-dev] [PATCH v5 1/3] lib/ring: apis to support configurable " Honnappa Nagarahalli
2019-10-17 20:39       ` Stephen Hemminger
2019-10-17 20:40       ` Stephen Hemminger
2019-10-17 20:08     ` [dpdk-dev] [PATCH v5 2/3] test/ring: add test cases for configurable element size ring Honnappa Nagarahalli
2019-10-17 20:08     ` [dpdk-dev] [PATCH v5 3/3] lib/ring: copy ring elements using memcpy partially Honnappa Nagarahalli
2019-10-21  0:22   ` [dpdk-dev] [RFC v6 0/6] lib/ring: APIs to support custom element size Honnappa Nagarahalli
2019-10-21  0:22     ` [dpdk-dev] [RFC v6 1/6] test/ring: use division for cycle count calculation Honnappa Nagarahalli
2019-10-23  9:49       ` Olivier Matz
2019-10-21  0:22     ` [dpdk-dev] [RFC v6 2/6] lib/ring: apis to support configurable element size Honnappa Nagarahalli
2019-10-23  9:59       ` Olivier Matz
2019-10-23 19:12         ` Honnappa Nagarahalli
2019-10-21  0:22     ` [dpdk-dev] [RFC v6 3/6] test/ring: add functional tests for configurable element size ring Honnappa Nagarahalli
2019-10-23 10:01       ` Olivier Matz
2019-10-23 11:12         ` Ananyev, Konstantin
2019-10-21  0:22     ` [dpdk-dev] [RFC v6 4/6] test/ring: add perf " Honnappa Nagarahalli
2019-10-23 10:02       ` Olivier Matz
2019-10-21  0:22     ` [dpdk-dev] [RFC v6 5/6] lib/ring: copy ring elements using memcpy partially Honnappa Nagarahalli
2019-10-21  0:23     ` [dpdk-dev] [RFC v6 6/6] lib/ring: improved copy function to copy ring elements Honnappa Nagarahalli
2019-10-23 10:05       ` Olivier Matz
2019-10-23  9:48     ` [dpdk-dev] [RFC v6 0/6] lib/ring: APIs to support custom element size Olivier Matz
2019-12-20  4:45   ` [dpdk-dev] [PATCH v7 00/17] " Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 01/17] test/ring: use division for cycle count calculation Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 02/17] lib/ring: apis to support configurable element size Honnappa Nagarahalli
2020-01-02 16:42       ` Ananyev, Konstantin
2020-01-07  5:35         ` Honnappa Nagarahalli
2020-01-07  6:00           ` Honnappa Nagarahalli
2020-01-07 10:21             ` Ananyev, Konstantin
2020-01-07 15:21               ` Honnappa Nagarahalli
2020-01-07 15:41                 ` Ananyev, Konstantin
2020-01-08  6:17                   ` Honnappa Nagarahalli
2020-01-08 10:05                     ` Ananyev, Konstantin [this message]
2020-01-08 23:40                       ` Honnappa Nagarahalli
2020-01-09  0:48                         ` Ananyev, Konstantin
2020-01-09 16:06                           ` Honnappa Nagarahalli
2020-01-13 11:53                             ` Ananyev, Konstantin
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 03/17] test/ring: add functional tests for rte_ring_xxx_elem APIs Honnappa Nagarahalli
2020-01-02 16:31       ` Ananyev, Konstantin
2020-01-07  5:13         ` Honnappa Nagarahalli
2020-01-07 16:03           ` Ananyev, Konstantin
2020-01-09  5:15             ` Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 04/17] test/ring: test burst APIs with random empty-full test case Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 05/17] test/ring: add default, single element test cases Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 06/17] test/ring: rte_ring_xxx_elem test cases for exact size ring Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 07/17] test/ring: negative test cases for rte_ring_xxx_elem APIs Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 08/17] test/ring: remove duplicate test cases Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 09/17] test/ring: removed unused variable synchro Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 10/17] test/ring: modify single element enq/deq perf test cases Honnappa Nagarahalli
2020-01-02 17:03       ` Ananyev, Konstantin
2020-01-07  5:54         ` Honnappa Nagarahalli
2020-01-07 16:13           ` Ananyev, Konstantin
2020-01-07 22:33             ` Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 11/17] test/ring: modify burst " Honnappa Nagarahalli
2020-01-02 16:57       ` Ananyev, Konstantin
2020-01-07  5:42         ` Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 12/17] test/ring: modify bulk " Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 13/17] test/ring: modify bulk empty deq " Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 14/17] test/ring: modify multi-lcore " Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 15/17] test/ring: adjust run-on-all-cores " Honnappa Nagarahalli
2020-01-02 17:00       ` Ananyev, Konstantin
2020-01-07  5:42         ` Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 16/17] lib/hash: use ring with 32b element size to save memory Honnappa Nagarahalli
2019-12-20  4:45     ` [dpdk-dev] [PATCH v7 17/17] lib/eventdev: use custom element size ring for event rings Honnappa Nagarahalli
2020-01-13 17:25   ` [dpdk-dev] [PATCH v8 0/6] lib/ring: APIs to support custom element size Honnappa Nagarahalli
2020-01-13 17:25     ` [dpdk-dev] [PATCH v8 1/6] test/ring: use division for cycle count calculation Honnappa Nagarahalli
2020-01-13 17:25     ` [dpdk-dev] [PATCH v8 2/6] lib/ring: apis to support configurable element size Honnappa Nagarahalli
2020-01-13 17:25     ` [dpdk-dev] [PATCH v8 3/6] test/ring: add functional tests for rte_ring_xxx_elem APIs Honnappa Nagarahalli
2020-01-13 17:25     ` [dpdk-dev] [PATCH v8 4/6] test/ring: modify perf test cases to use " Honnappa Nagarahalli
2020-01-13 17:25     ` [dpdk-dev] [PATCH v8 5/6] lib/hash: use ring with 32b element size to save memory Honnappa Nagarahalli
2020-01-13 17:25     ` [dpdk-dev] [PATCH v8 6/6] lib/eventdev: use custom element size ring for event rings Honnappa Nagarahalli
     [not found]       ` <1578977880-13011-1-git-send-email-robot@bytheb.org>
     [not found]         ` <VE1PR08MB5149BE79083CD66A41CBD6D198340@VE1PR08MB5149.eurprd08.prod.outlook.com>
2020-01-14 15:12           ` [dpdk-dev] FW: || pw64572 " Aaron Conole
2020-01-14 16:51             ` Aaron Conole
2020-01-14 19:35               ` Honnappa Nagarahalli
2020-01-14 20:44                 ` Aaron Conole
2020-01-15  0:55                   ` Honnappa Nagarahalli
2020-01-15  4:43                   ` Honnappa Nagarahalli
2020-01-15  5:05                     ` Honnappa Nagarahalli
2020-01-15 18:22                       ` Aaron Conole
2020-01-15 18:38                         ` Honnappa Nagarahalli
2020-01-16  5:27                           ` Honnappa Nagarahalli
2020-01-16  5:25   ` [dpdk-dev] [PATCH v9 0/6] lib/ring: APIs to support custom element size Honnappa Nagarahalli
2020-01-16  5:25     ` [dpdk-dev] [PATCH v9 1/6] test/ring: use division for cycle count calculation Honnappa Nagarahalli
2020-01-16  5:25     ` [dpdk-dev] [PATCH v9 2/6] lib/ring: apis to support configurable element size Honnappa Nagarahalli
2020-01-17 16:34       ` Olivier Matz
2020-01-17 16:45         ` Honnappa Nagarahalli
2020-01-17 18:10           ` David Christensen
2020-01-18 12:32           ` Ananyev, Konstantin
2020-01-18 15:01             ` Honnappa Nagarahalli
2020-01-16  5:25     ` [dpdk-dev] [PATCH v9 3/6] test/ring: add functional tests for rte_ring_xxx_elem APIs Honnappa Nagarahalli
2020-01-17 17:03       ` Olivier Matz
2020-01-18 16:27         ` Honnappa Nagarahalli
2020-01-16  5:25     ` [dpdk-dev] [PATCH v9 4/6] test/ring: modify perf test cases to use " Honnappa Nagarahalli
2020-01-17 17:12       ` Olivier Matz
2020-01-18 16:28         ` Honnappa Nagarahalli
2020-01-16  5:25     ` [dpdk-dev] [PATCH v9 5/6] lib/hash: use ring with 32b element size to save memory Honnappa Nagarahalli
2020-01-17 20:27       ` David Marchand
2020-01-17 20:54         ` Honnappa Nagarahalli
2020-01-17 21:07           ` David Marchand
2020-01-17 22:24             ` Wang, Yipeng1
2020-01-16  5:25     ` [dpdk-dev] [PATCH v9 6/6] lib/eventdev: use custom element size ring for event rings Honnappa Nagarahalli
2020-01-17 14:41       ` Jerin Jacob
2020-01-17 16:12         ` David Marchand
2020-01-16 16:36     ` [dpdk-dev] [PATCH v9 0/6] lib/ring: APIs to support custom element size Honnappa Nagarahalli
2020-01-17 12:14       ` David Marchand
2020-01-17 13:34         ` Jerin Jacob
2020-01-17 16:37           ` Mattias Rönnblom
2020-01-17 14:28         ` Honnappa Nagarahalli
2020-01-17 14:36           ` Honnappa Nagarahalli
2020-01-17 16:15           ` David Marchand
2020-01-17 16:32             ` Honnappa Nagarahalli
2020-01-17 17:15     ` Olivier Matz
2020-01-18 19:32   ` [dpdk-dev] [PATCH v10 " Honnappa Nagarahalli
2020-01-18 19:32     ` [dpdk-dev] [PATCH v10 1/6] test/ring: use division for cycle count calculation Honnappa Nagarahalli
2020-01-18 19:32     ` [dpdk-dev] [PATCH v10 2/6] lib/ring: apis to support configurable element size Honnappa Nagarahalli
2020-01-18 19:32     ` [dpdk-dev] [PATCH v10 3/6] test/ring: add functional tests for rte_ring_xxx_elem APIs Honnappa Nagarahalli
2020-01-18 19:32     ` [dpdk-dev] [PATCH v10 4/6] test/ring: modify perf test cases to use " Honnappa Nagarahalli
2020-01-18 19:32     ` [dpdk-dev] [PATCH v10 5/6] lib/hash: use ring with 32b element size to save memory Honnappa Nagarahalli
2020-01-18 19:32     ` [dpdk-dev] [PATCH v10 6/6] eventdev: use custom element size ring for event rings Honnappa Nagarahalli
2020-01-19 19:31     ` [dpdk-dev] [PATCH v10 0/6] lib/ring: APIs to support custom element size David Marchand

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