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

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2017-04-05 08:34, Singh, Jasvinder:
> Hi Thomas,
> 
> From: Thomas Monjalon [mailto:thomas.monjalon@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?