Re: [dpdk-dev] [PATCH] drivers: cleanup unnecessary global variables

[Olivier Matz <olivier.matz@6wind.com>]

Le 25 avril 2018 17:52:00 GMT+02:00, Pavan Nikhilesh <pbhagavatula@caviumnetworks.com> a écrit :
>On Mon, Apr 23, 2018 at 11:00:09AM +0200, Olivier Matz wrote:
>> On Fri, Apr 20, 2018 at 12:21:59AM +0530, Pavan Nikhilesh wrote:
>> > Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
>> > ---
>> >  drivers/bus/dpaa/base/fman/netcfg_layer.c     | 5 -----
>> >  drivers/bus/dpaa/base/qbman/bman_driver.c     | 4 ++--
>> >  drivers/bus/dpaa/base/qbman/qman.c            | 2 +-
>> >  drivers/bus/dpaa/base/qbman/qman_driver.c     | 4 ++--
>> >  drivers/bus/dpaa/base/qbman/qman_priv.h       | 1 -
>> >  drivers/bus/dpaa/dpaa_bus.c                   | 2 +-
>> >  drivers/bus/fslmc/qbman/qbman_portal.c        | 3 +--
>> >  drivers/bus/fslmc/qbman/qbman_portal.h        | 1 -
>> >  drivers/net/i40e/i40e_flow.c                  | 2 +-
>> >  drivers/net/qede/base/bcm_osal.c              | 2 +-
>> >  drivers/raw/skeleton_rawdev/skeleton_rawdev.c | 2 +-
>> >  lib/librte_net/net_crc_neon.h                 | 4 ++--
>> >  12 files changed, 12 insertions(+), 20 deletions(-)
>>
>> [...]
>>
>> > diff --git a/lib/librte_net/net_crc_neon.h
>b/lib/librte_net/net_crc_neon.h
>> > index 63fa1d4a1..cb3da72ed 100644
>> > --- a/lib/librte_net/net_crc_neon.h
>> > +++ b/lib/librte_net/net_crc_neon.h
>> > @@ -21,8 +21,8 @@ struct crc_pmull_ctx {
>> >  	uint64x2_t rk7_rk8;
>> >  };
>> >
>> > -struct crc_pmull_ctx crc32_eth_pmull __rte_aligned(16);
>> > -struct crc_pmull_ctx crc16_ccitt_pmull __rte_aligned(16);
>> > +static struct crc_pmull_ctx crc32_eth_pmull __rte_aligned(16);
>> > +static struct crc_pmull_ctx crc16_ccitt_pmull __rte_aligned(16);
>> >
>> >  /**
>>
>> Not sure it will still work after that.
>>
>> From what I see, these global variables are initialized once in
>> rte_net_crc_neon_init, and used as a const parameter in
>> crc32_eth_calc_pmull().
>>
>> Changing them to static will create an instance of these variables
>for
>> each included file, which is not what we want.
>>
>> I think that the proper way to solve it would be to add the
>definition
>> in a new .c file, and only have a declaration in the .h.
>>
>>
>Hi Olivier,
>
>Thanks for the heads up, the second solution seems more viable and
>while
>implementing it I faced few Issues. GCC doesnt suport const vector
>instructions
>i.e. the following assignment throw as compiler error.
>
>	static const struct crc_pmull_ctx crc32_eth_pmull = {
>  		.rk1_rk2 = vld1q_u64((uint64_t[2]){0xccaa009eLLU, 0x1751997d0LLU}),
>  		.rk5_rk6 = vld1q_u64((uint64_t[2]){0xccaa009eLLU, 0x163cd6124LLU}),
> 		.rk7_rk8 = vld1q_u64((uint64_t[2]){0x1f7011640LLU, 0x1db710641LLU}),
>	} __rte_aligned(16);
>
>I have gotten path the error by modifying struct crc_pmull_ctx as
>follows:
>
>	struct crc_pmull_ctx {
>	        union {
>	                uint64_t rk12[2];
>	                uint64x2_t rk1_rk2;
>	        };
>	        union {
>	                uint64_t rk56[2];
>	                uint64x2_t rk5_rk6;
>	        };
>	        union {
>	                uint64_t rk78[2];
>	                uint64x2_t rk7_rk8;
>	        };
>	};
>
>	static const struct crc_pmull_ctx crc32_eth_pmull __rte_aligned(16) =
>{
>	        .rk12 = {0xccaa009eLLU, 0x1751997d0LLU},
>	        .rk56 = {0xccaa009eLLU, 0x163cd6124LLU},
>	        .rk78 = {0x1f7011640LLU, 0x1db710641LLU},
>	};
>
>	static const struct crc_pmull_ctx crc16_ccitt_pmull __rte_aligned(16)
>= {
>	        .rk12 = {0x189aeLLU, 0x8e10LLU},
>	        .rk56 = {0x189aeLLU, 0x114aaLLU},
>	        .rk78 = {0x11c581910LLU, 0x10811LLU},
>	};
>
>I have checked the hex dump of the assignment with the current code and
>the
>above piece of code and they are similar.
>
>Let me know if my solution seems viable I will send the v2.
>

Looks good, just wondering about possible endianness issues. Is arm architecture supported with both little and big endian in dpdk ?


>> An even better way would be to make variable const and initialize it
>> with its content. It could even enhance performance. Something like:
>>
>> net_crc_neon.h:
>>
>> static const struct crc_pmull_ctx crc32_eth_pmull = {
>>       <values...>
>> } __rte_aligned(16);
>>
>> static const struct crc_pmull_ctx crc16_ccitt_pmull = {
>>       <values...>
>> } __rte_aligned(16);
>>
>
>Thanks,
>Pavan.