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

[Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>]

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.

> 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.