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Date: Fri, 18 Mar 2016 15:11:18 +0100
From: Jan Viktorin <viktorin@rehivetech.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: Jerin Jacob <jerin.jacob@caviumnetworks.com>, Tomasz Kulasek
 <tomaszx.kulasek@intel.com>, dev@dpdk.org, jianbo.liu@linaro.org
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Subject: Re: [dpdk-dev] [PATCH] arm: detect NEON by RTE_MACHINE_CPUFLAG_NEON
	flag only
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On Fri, 18 Mar 2016 14:49:57 +0100
Thomas Monjalon <thomas.monjalon@6wind.com> wrote:

> 2016-03-18 13:00, Jan Viktorin:
> > The RTE_MACHINE_CPUFLAG_NEON was only a result of the gcc testing.
> > However, the target CPU may not support NEON or the user can disable to
> > use it (as it does not always improve the performance).
> > 
> > The RTE_MACHINE_CPUFLAG_NEON detection is now based on both, the
> > __ARM_NEON_FP feature from gcc and CONFIG_RTE_ARCH_ARM_NEON from
> > the .config. The memcpy implemention is driven by
> > RTE_MACHINE_CPUFLAG_NEON, so the reason to disable neon is hidden for
> > the actual code.
> > 
> > Signed-off-by: Jan Viktorin <viktorin@rehivetech.com>
> > ---
> > 
> > I can also include this one:
> > 
> > examples/l3fwd/l3fwd_em.c:253:#elif defined(__ARM_NEON)  
> 
> Yes please.
> I will set my patch as superseded.
> 

OK, I will send v2.

By the way, for Intel-related code, it is also common to check eg.
__SSE2__ instead of the RTE_MACHINE_CPUFLAG_SSE2. That's probably a
source of confusion for new code, newcomers and adding new platforms.

As for me, I've had known about the CPUFLAGs... But I could hardly see
those in the DPDK code. It looks like the features are detected by
unused... And IMHO this is the reason why we are confused here.

Regards
Jan