Re: [dpdk-dev] [PATCH] examples/l3fwd: fix em mode datapath selection

[Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>]

>-----Original Message-----
>From: dev <dev-bounces@dpdk.org> On Behalf Of Thomas Monjalon
>Sent: Tuesday, April 23, 2019 2:05 PM
>To: Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>
>Cc: dev@dpdk.org; Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Marko
>Kovacevic <marko.kovacevic@intel.com>; Ori Kam <orika@mellanox.com>;
>Bruce Richardson <bruce.richardson@intel.com>; Pablo de Lara
><pablo.de.lara.guarch@intel.com>; Radu Nicolau <radu.nicolau@intel.com>;
>Akhil Goyal <akhil.goyal@nxp.com>; Tomasz Kantecki
><tomasz.kantecki@intel.com>; stable@dpdk.org
>Subject: Re: [dpdk-dev] [PATCH] examples/l3fwd: fix em mode datapath
>selection
>
>23/04/2019 04:47, Pavan Nikhilesh Bhagavatula:
>>From: Thomas Monjalon <thomas@monjalon.net>
>> >10/04/2019 09:29, Pavan Nikhilesh Bhagavatula:
>> >> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
>> >>
>> >> Currently, l3wfd em mode has two datapath modes em_sequential and
>> >> em_hlm. We can select either of them by defining
>> >NO_HASH_MULTI_LOOKUP
>> >> to one or zero.
>> >> The code checks if NO_HASH_MULTI_LOOKUP is defined or not instead
>> >> of checking for the value.
>> >>
>> >> Fixes: 52c97adc1f0f ("examples/l3fwd: fix exact match performance")
>> >> Cc: stable@dpdk.org
>> >>
>> >> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
>> >> ---
>> >> --- a/examples/l3fwd/l3fwd_em.c
>> >> +++ b/examples/l3fwd/l3fwd_em.c
>> >>  #if defined RTE_ARCH_X86 || defined RTE_MACHINE_CPUFLAG_NEON
>-#if
>> >> defined(NO_HASH_MULTI_LOOKUP)
>> >> +#if NO_HASH_MULTI_LOOKUP
>> >
>> >A quick grep shows that it used in another place with #ifdef:
>> >
>> >examples/l3fwd/l3fwd.h:#if !defined(NO_HASH_MULTI_LOOKUP) &&
>> >defined(RTE_MACHINE_CPUFLAG_NEON)
>> >
>> >
>>
>> #if !defined(NO_HASH_MULTI_LOOKUP) &&
>> defined(RTE_MACHINE_CPUFLAG_NEON) #define
>NO_HASH_MULTI_LOOKUP 1
>> #endif
>>
>> This macro is used to set l3fwd_em_sequential as the default EM
>> datapath on AARCH64 as its performance is better.
>> (http://patches.dpdk.org/patch/49372/)
>>
>> make -C examples/l3fwd           #Selects l3fwd_em_sequential by default on
>AARCH 64
>>
>> Currently, we cannot select em_hlm without manually editing the macro
>> as using the below command still sets em_sequential as the default
>> datapath because the macro modified in the patch that selects the datapath
>checks if NO_HASH_MULTI_LOOKUP is defined or not rather than its value.
>>
>> EXTRA_CFLAGS='-DNO_HASH_MULTI_LOOKUP=0' make -C examples/l3fwd
>>
>> I hope I cleared up things a bit.
>
>In my understanding, we should check the value in the other case too, instead
>of #if defined.

That will lead to undefined and redefined error:

[dpdk] # make -C examples/l3fwd
make: Entering directory '/root/pavan/dpdk-int/examples/l3fwd'
  CC main.o
  CC l3fwd_lpm.o
In file included from /root/dpdk/examples/l3fwd/l3fwd_lpm.c:28:0:
/root/dpdk/examples/l3fwd/l3fwd.h:14:6: error: "NO_HASH_MULTI_LOOKUP" is not defined, evaluates to 0 [-Werror=undef]
 #if !NO_HASH_MULTI_LOOKUP && defined(RTE_MACHINE_CPUFLAG_NEON)

[dpdk] # EXTRA_CFLAGS='-DNO_HASH_MULTI_LOOKUP=0' make -C examples/l3fwd
make: Entering directory '/root/dpdk/examples/l3fwd'
  CC main.o                                                                                       ]
 #define NO_HASH_MULTI_LOOKUP 1
 n file included from /root/dpdk/examples/l3fwd/l3fwd_lpm.c:28:0:
<command-line>:0:0: note:
                                                                                                  ]
 #define NO_HASH_MULTI_LOOKUP 1is the location of the previous definition

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