[dpdk-dev] [PATCH v9 0/3] librte_net: add crc computation support

Richardson, Bruce bruce.richardson at intel.com
Wed Apr 5 11:37:21 CEST 2017



> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Thomas Monjalon
> Sent: Wednesday, April 5, 2017 10:01 AM
> To: Singh, Jasvinder <jasvinder.singh at intel.com>
> Cc: dev at dpdk.org; olivier.matz at 6wind.com; Doherty, Declan
> <declan.doherty at intel.com>; De Lara Guarch, Pablo
> <pablo.de.lara.guarch at intel.com>
> Subject: Re: [dpdk-dev] [PATCH v9 0/3] librte_net: add crc computation
> support
> 
> 2017-04-05 08:34, Singh, Jasvinder:
> > Hi Thomas,
> >
> > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com]
> > > 2017-03-30 17:15, Jasvinder Singh:
> > > > In some applications, CRC (Cyclic Redundancy Check) needs to be
> > > > computed or updated during packet processing operations. This
> > > > patchset adds software implementation of some common standard CRCs
> > > > (32-bit Ethernet CRC as per Ethernet/[ISO/IEC 8802-3] and 16-bit
> > > > CCITT-CRC [ITU-T
> > > X.25]).
> > > > Two versions of each 32-bit and 16-bit CRC calculation are proposed.
> > > >
> > > > The first version presents a fast and efficient CRC generation on
> > > > IA processors by using the carry-less multiplication instruction
> > > > PCLMULQDQ (i.e SSE4.2 instrinsics). In this implementation, a
> > > > parallelized folding approach has been used to first reduce an
> > > > arbitrary length buffer to a small fixed size length buffer (16
> > > > bytes) with the
> > > help of precomputed constants.
> > > > The resultant single 16-bytes chunk is further reduced by Barrett
> > > > reduction method to generate final CRC value. For more details on
> > > > the implementation, see reference [1].
> > > >
> > > > The second version presents the fallback solution to support the
> > > > CRC generation without needing any specific support from CPU (for
> > > > examples-
> > > > SSE4.2 intrinsics). It is based on generic Look-Up Table(LUT)
> > > > algorithm that uses precomputed 256 element table as explained in
> > > reference[2].
> > > >
> > > > During intialisation, all the data structures required for CRC
> > > > computation are initialised. Also, x86 specific crc implementation
> > > > (if supported by the platform) or scalar version is enabled.
> > >
> > > As you can see in patchwork, it does not compile on FreeBSD:
> > > 	http://dpdk.org/ml/archives/test-report/2017-April/016943.html
> >
> > As I stated in the cover letter  notes as well that The patchset build
> > fails on clang version earlier than 3.7.0 due to missing intrinsics and
> this issue is listed in DPDK known issue section. FreeBSD build on gcc
> target should work fine.
> 
> Ah, I have not seen this explanation.
> 
> However, we cannot let the build fails.
> It is a blocker for patch admission.
> 
> Can you, at least, disable the code for some compiler versions?

Hi Jasvinder,

Any chance a work-around for this issue. The default compiler on BSD is clang, and the BSD 10 series of releases uses v3.4. This means this functionality will be unavailable for anyone using DPDK from BSD ports on BSD 10.

/Bruce



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