Re: [dpdk-dev] compile dpdk with no avx

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Nov 12, 2014 at 10:23:49AM -0500, Neil Horman wrote:
> On Wed, Nov 12, 2014 at 02:24:10PM +0000, De Lara Guarch, Pablo wrote:
> > 
> > 
> > > -----Original Message-----
> > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Masaru Oki
> > > Sent: Wednesday, November 12, 2014 1:48 PM
> > > To: Yaron Illouz
> > > Cc: <dev@dpdk.org>
> > > Subject: Re: [dpdk-dev] compile dpdk with no avx
> > > 
> > > Hi,
> > > 
> > > Some libraries need AVX instruction, but if you don't use, it can disable.
> > >   e.g. CONFIG_RTE_LIBRTE_IXGBE_PMD=n in config file.
> > > 
> > > 
> > > 2014-11-12 21:45 GMT+09:00 Yaron Illouz <yaroni@radcom.com>:
> > > > Hi
> > > >
> > > >
> > > >
> > > > I use dpdk in my product. I can't change my dpdk version.
> > > >
> > > > I compile it on a server that have avx.
> > > >
> > > > Most of the time, it run on machine that have avx, but not always.
> > > >
> > > >
> > > >
> > > > When running the product on a machine with no avx, it crash on illegal
> > > > instruction.
> > > >
> > > > The current solution is to build it on a computer with no avx.
> > > >
> > > >
> > > >
> > > > Is there a compilation flag to disable avx? So it doesn't matter on
> > > > which computer I compiled it.
> > 
> > Basically, you are looking at cross-compiling DPDK. One thing you could do
> >  is go to one of the config files (i.e. defconfig_x86-64-native-linuxapp-gcc) 
> > and change CONFIG_RTE_MACHINE, from "native" to one of the
> >  micro-architectures that do not have avx, such as "wsm" (Westmere).
> > 
> What version of dpdk are you running?  We fixed this a while ago with
> commits 8777aabc538fdac24457958eaab929f33d6c4cdf and
> 074f54ad03ee0c84dcae235933e2b426208fe591.  They do runtime checking for
> availability of the AVX and SSE3 instructions and only exeucte paths using those
> instructions if the running cpu supports them.  Note that you are still required
> to build for the default arch.
> Neil
> 

Hi Neil,

those commits only fix the cases where we compile the code generically, and have
specific runtime code paths. However, when compiling for a native target the
compiler will freely use AVX instructions when it feels it will lead to faster
code. There is no run-time checking we can do to avoid this, hence the need
for changing the build-time configuration.

/Bruce

> > Regards,
> > Pablo
> > 
> > > >
> > > >
> > > >
> > > > Compile flag
> > > >
> > > > defconfig_x86_64-default-linuxapp-gcc
> > > >
> > > >
> > > >
> > > > Dpdk version
> > > >
> > > > PACKAGE_VERSION_MAJOR_NUMBER=1
> > > >
> > > > PACKAGE_VERSION_MINOR_NUMBER=6
> > > >
> > > > PACKAGE_VERSION_PATCH_NUMBER=0
> > > >
> > > > PACKAGE_VERSION_BUILD_NUMBER=18
> > > >
> > > >
> > > >
> > > > Gcc version
> > > >
> > > > gcc (GCC) 4.4.6 20120305 (Red Hat 4.4.6-4)
> > > >
> > > >
> > > >
> > > > OS
> > > >
> > > > CentOS release 6.3 (Final)
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >