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From: Ferruh Yigit <ferruh.yigit@intel.com>
To: Bruce Richardson <bruce.richardson@intel.com>,
	Thomas Monjalon <thomas@monjalon.net>
Cc: dev@dpdk.org, techboard@dpdk.org
Subject: Re: [dpdk-dev] [dpdk-techboard] [PATCH 1/1] doc: add deprecation notice for CPU build flags
Date: Thu, 6 Aug 2020 22:41:23 +0100
Message-ID: <27d08eb2-5f66-e385-3d05-39ac317ece89@intel.com> (raw)
In-Reply-To: <20200805164504.GE1716@bricha3-MOBL.ger.corp.intel.com>

On 8/5/2020 5:45 PM, Bruce Richardson wrote:
> On Wed, Aug 05, 2020 at 05:15:31PM +0200, Thomas Monjalon wrote:
>> 05/08/2020 17:07, Bruce Richardson:
>>> On Wed, Aug 05, 2020 at 04:57:42PM +0200, Thomas Monjalon wrote:
>>>> 05/08/2020 16:21, Bruce Richardson:
>>>>> The RTE_MACHINE_CPUFLAGS_* macros in DPDK build just duplicate info from
>>>>> the compiler macros, so we can remove them and just use the compiler
>>>>> versions directly.
>>>>>
>>>>> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
>>>>> ---
>>>>> --- a/doc/guides/rel_notes/deprecation.rst
>>>>> +++ b/doc/guides/rel_notes/deprecation.rst
>>>>> +* build macros: The macros defining RTE_MACHINE_CPUFLAG_* will be removed
>>>>> +  from the build. The information provided by these macros is available
>>>>> +  through standard compiler macros. For example, RTE_MACHINE_CPUFLAG_SSE3
>>>>> +  duplicates the compiler-provided macro __SSE3__.
>>>>
>>>> I see 2 advantages of having alias:
>>>> 	- if 2 compilers differ, we can manage
>>>> 	- we can find all such macros with grep RTE_MACHINE_CPUFLAG
>>>>
>>>
>>> Sure, if you think it's worthwhile keeping them, we can do so. It's just
>>> right now they seem to be largely a waste of space. For #2, I'm not sure
>>> when we would want to grep for them all, except possibly to remove them.
>>> :-)
>>
>> For instance, in a lib, I grep where we have CPU specific code.
>>
>> We probably need more opinions, I can change my mind.
>>
> Yes, we need some more opinions here.
> 
> For the above point, yes it's useful to be able to grep for these things,
> but it does assume that everybody uses the DPDK-defines and doesn't use the
> compiler ones directly. There are a few instances where there seems to be
> x86, ARM or PPC compiler flags already directly used in the code.
> 
> As well as brevity, the other big reason I see for removing them is to
> avoid having to maintain these lists of flags for future use. Right now,
> with -march=skylake-avx512, gcc will define 7 different AVX feature flags.
> DPDK, on the other hand, only provides equivalent defines for 3 of them.
> We have no automatic way of pulling all newly added flags from gcc/clang
> into our build, so we just add them on an as-needed basis, which makes it
> more awkward for those adding new features that may depend on the flags. If
> we always try to add in all flags to keep things in sync, we are just
> duplicating the efforts the compiler authors have already done for us, and
> wasting the effort for those flags that are unused.
> 

Sounds reasonable,

Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>


  parent reply	other threads:[~2020-08-06 21:41 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-05 14:21 [dpdk-dev] [PATCH 0/1] RFC: remove build-type CPU flag macros Bruce Richardson
2020-08-05 14:21 ` [dpdk-dev] [PATCH 1/1] doc: add deprecation notice for CPU build flags Bruce Richardson
2020-08-05 14:23   ` Jerin Jacob
2020-08-05 14:57   ` [dpdk-dev] [dpdk-techboard] " Thomas Monjalon
2020-08-05 15:07     ` Bruce Richardson
2020-08-05 15:15       ` Thomas Monjalon
2020-08-05 16:45         ` Bruce Richardson
2020-08-05 17:02           ` Thomas Monjalon
2020-08-06 16:01             ` Thomas Monjalon
2020-08-06 21:41           ` Ferruh Yigit [this message]
2020-08-07 13:48             ` Thomas Monjalon

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