Re: [dpdk-dev] [PATCH v2 0/2] dpdk: Allow for dynamic enablement of some isolated features

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, Jul 30, 2014 at 12:03:38PM -0700, Venky Venkatesan wrote:
> Neil,
> 
> >Hey all-
> >         I've been trying to update the fedora dpdk package to support VFIO
> >enabled drivers and ran into a problem in which ixgbe didn't compile because the
> >rxtx_vec code uses sse4.2 instruction intrinsics, which aren't supported in the
> >default config I have.  I tried to remedy this by replacing the intrinsics with
> >the __builtin macros, but it was pointed out (correctly), that this doesn't work
> >properly.  So this is my second attempt, which I actually like a bit better.  I
> >noted that code that uses intrinsics (ixgbe and the acl library), don't need to
> >have those instructions turned on build-wide.  Rather, we can just enable the
> >instructions in the specific code we want to build with support for that, and
> >test for instruction support dynamically at run time.  This allows me to build
> >the dpdk for a generic platform, but in such a way that some optimizations can
> >be used if the executing cpu supports them at run time.
> >
> >Change notes:
> >
> >v2)
> >	* Added Log messages to run time check failures per Konstantin
> >	* Removed run time check caching in acl per Konstantin
> >
> >Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> >CC: Thomas Monjalon <thomas.monjalon@6wind.com>
> >
> 
> One possible change to look at - the _mm_shuffle_epi8 is something that is
> available all the way from SSSE3, so you should be able to leave that in.
> The SSE4.2 dependency is only for the popcount (and __builtin_popcountll
> will work for that anyway). That should make things simpler.
> 
Hmm, I'd just as soon leave the use of the __builtin_* intrinsics alone at this
point, as I'd like to focus on the optional enablement of these features at run
time more than making them work in all cases (at least for right now), as I'd
like a distribution build to take advantage of the accelerated instructions when
they're available at run time..  But if we can reduce the intrinsic requirement
to ssse3 in some locations that would be good.  Let me experiment and I'll post
a v3
Neil

> -Venky
>