[dpdk-dev] [PATCH 3/4] eal/arm: Enable lpm/table/pipeline libs

[Ananyev, Konstantin]

Hi Jerin,

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Jerin Jacob
> Sent: Thursday, December 03, 2015 9:34 AM
> To: Thomas Monjalon
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 3/4] eal/arm: Enable lpm/table/pipeline libs
> 
> On Wed, Dec 02, 2015 at 05:57:10PM +0100, Thomas Monjalon wrote:
> > 2015-12-02 22:23, Jerin Jacob:
> > > On Wed, Dec 02, 2015 at 05:40:13PM +0100, Thomas Monjalon wrote:
> > > > 2015-12-02 20:04, Jerin Jacob:
> > > > > On Wed, Dec 02, 2015 at 09:13:51PM +0800, Jianbo Liu wrote:
> > > > > > On 2 December 2015 at 18:39, Jerin Jacob <jerin.jacob at caviumnetworks.com> wrote:
> > > > > > > AND they include "rte_lpm.h"(it internally includes rte_vect.h)
> > > > > > > that lead to multiple definition and its not good.
> > > > > > >
> > > > > > But you will have similar issue since "typedef int32x4_t __m128i"
> > > > > > appears in both your patch and this header file.
> > > > >
> > > > > I just tested it, it won't break, back to back "typedef int32x4_t __m128i"
> > > > > is fine(unlike inline function).
> > > > >
> > > > > my intention to keep __m128i "as is"  because changing the __m128i to rte_???
> > > > > something would break the ABI.
> > > >
> > > > Isn't it already broken in 2.2?
> > >
> > > Does it mean, You would like to have rte_128i(or similar) kind of
> > > abstraction to represent 128bit SIMD variable in DPDK?
> >
> > If you are convinced that it is the best way to write a generic code, yes.
> 
> I grep-ed through DPDK API list to see the dependency with SIMD in API
> definition.I see only rte_lpm_lookupx4 API has SIMD dependency in API
> definition.
> 
> I believe that's the root cause of the problem. IMO, The
> better way to fix this would be to remove __m128i from API and have more
> general representation to remove the architecture dependency from API
> 
> something like this,
> 
> rte_lpm_lookupx4(const struct rte_lpm *lpm, uint32_t *ip, uint16_t
> hop[4], uint16_t defv)
> 
> instead of
> 
> rte_lpm_lookupx4(const struct rte_lpm *lpm, __m128i ip, uint16_t
> hop[4],  uint16_t defv)

The idea for that function was that rte_lpm_lookupx4() accepts 4 IPv4 addresses that are:
1. already in 128bit register
2. 'prepared' - byte swap is already done for them if needed. 

About ways to fix  __m128i dependency: as I can see x86 and arm DPDK code
already has xmm_t typedef:
 
$ find lib -type f | xargs grep xmm_t | grep typedef
lib/librte_eal/common/include/arch/x86/rte_vect.h:typedef __m128i xmm_t;
lib/librte_eal/common/include/arch/arm/rte_vect.h:typedef int32x4_t xmm_t;

Why not to  change rte_lpm_lookupx4() to accept xmm_t as input parameter.
As I understand it would solve the problem, and wouldn't introduce any API/ABI breakage, right?

Konstantin

> 
> Now I am not sure why this API was created like this, from l3fwd.c
> example, it looks to accommodate the IPV4 byte swap[1]. If it's true,
> maybe we can have eal byte swap abstraction for optimized byte swap on
> memory for 4 IP address in one shot
> 
> or
> 
> Have rte_lpm_lookupx4 take an argument for byte swap or not ?
> 
> or
> 
> something similar?
> 
> Thoughts ?
> 
> [1]
> const  __m128i bswap_mask = _mm_set_epi8(12, 13, 14, 15, 8, 9, 10, 11,
>                                                 4, 5, 6, 7, 0, 1, 2, 3);
> /* Byte swap 4 IPV4 addresses. */
> dip = _mm_shuffle_epi8(dip, bswap_mask);
> 
> Jerin
> 
> > I think the most important question is to know what is the best solution
> > for performance and maintainability. The API/ABI questions will be considered
> > after.
> >
> > Thanks for your involvement guys.