Re: [dpdk-dev] [PATCH v2] net/i40e: Eliminate weak symbols in i40e_rxtx.c

["David Harton (dharton)" <dharton@cisco.com>]

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@intel.com>
> Sent: Tuesday, June 04, 2019 12:00 PM
> To: Bruce Richardson <bruce.richardson@intel.com>; David Harton (dharton)
> <dharton@cisco.com>
> Cc: dev@dpdk.org; beilei.xing@intel.com; qi.z.zhang@intel.com
> Subject: Re: [dpdk-dev] [PATCH v2] net/i40e: Eliminate weak symbols in
> i40e_rxtx.c
> 
> On 5/16/2019 3:08 PM, Bruce Richardson wrote:
> > On Wed, May 15, 2019 at 12:13:46PM -0400, David Harton wrote:
> >> Use of weak symbols can hide makefile errors especially when custom
> >> makefiles are used.  Removing the use of weak symbols to avoid a stub
> >> function being linked in production code.
> >>
> >> Signed-off-by: David Harton <dharton@cisco.com>
> >> ---
> >>
> >> v2 - added CC_AVX2_SUPPORT check to code enabling avx2 vectors
> >>
> > Testing a few compiles here, this breaks when vector mode is disabled,
> > because it's possible that CC_AVX2_SUPPORT=1 when VECTOR=n. I'd
> > suggest adding "ifeq ($(CONFIG_RTE_LIBRTE_I40E_INC_VECTOR),y) ...
> > endif" around the block in the makefile checking for AVX2 support, so
> > that we never set AVX2 unless we have vector support.
> 
> Concern is this is pushing vectorization support more to compile time
> configuration. Do we really have to select if to use vector PMD or not in
> compile time?
> 
> Can't we get rid of the 'CONFIG_RTE_LIBRTE_I40E_INC_VECTOR' config option
> completely? As done in the ICE driver now.
> 
> Isn't it better to compile vectorization support in as much as possible
> and do the vector or scalar path selection in runtime, this patch may
> prevent us to do that, weak functions enables us being more dynamic.

Choosing a vector dynamically can be done without the use of weak symbols.

IMHO, weak symbols should really be used for cross library support where a user wants to override a 3rd party function not within a lib.  In fact the weak symbol usage may preclude supporting all the variants you might need/want to select.

> 
> >
> > With this change, you can include my ack in v3.
> >
> > /Bruce
> >
> > Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> >