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.
> 
> -Venky
> 

ugh, actually both the ixgbe and acl libraries use the popcnt instruction, so I
think I'd rather just keep the sse4.2 instruction set as it is, unless you think
the __builtin_popcnt is equally performant.

Neil