Hi Honnappa, >-----Original Message----- >From: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com> >Sent: Tuesday 11 August 2020 06:37 >To: Power, Ciara <ciara.po...@intel.com>; dev@dpdk.org >Cc: Richardson, Bruce <bruce.richard...@intel.com>; nd <n...@arm.com>; >Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>; nd ><n...@arm.com> >Subject: RE: [dpdk-dev] [PATCH 20.11 00/12] add max SIMD bitwidth to EAL > >Hi Ciara, > I have not reviewed other patches in this series yet. Few questions >inline. > >> -----Original Message----- >> From: dev <dev-boun...@dpdk.org> On Behalf Of Ciara Power >> Sent: Friday, August 7, 2020 10:59 AM >> To: dev@dpdk.org >> Cc: bruce.richard...@intel.com; Ciara Power <ciara.po...@intel.com> >> Subject: [dpdk-dev] [PATCH 20.11 00/12] add max SIMD bitwidth to EAL >> >> A number of components in DPDK have optional AVX-512 or other vector >> code paths which can be selected at runtime. Rather than having each >> component provide its own mechanism to select a code path, this >> patchset adds support for a single setting to control what code paths are >used. >Do you mean that all the components will have to use AVX-512? >IMO, different libraries might behave differently to the use of different >vector >sizes. Are we taking away the ability to use different vector sizes for >different >components. >
No, this setting is a max bitwidth which can be set by apps using the EAL API based on what is best for the usage in their apps, or by the user with an EAL flag, but each library is still free to choose it's own best path, subject to it not being longer than the specified max. For example, if the max bitwidth is set to 512, a library can still choose to use a 256-bit path over a 512 one if its advantageous. >> This can be used to enable some non-default code paths e.g. ones using >> AVX- 512, but also to limit the code paths to certain vector widths, >> or to scalar code only, which is useful for testing. >> >> The max SIMD bitwidth setting can be set by the app itself through use >> of the available API, or can be overriden by a commandline argument >> passed by the user. >Arm platforms support SVE (scalable vector extensions) feature. With this >feature, the code is agnostic to the vector size. i.e. same code can run on >various vector sizes. There is no code yet in DPDK with this feature. But, it >will >be added in the near future. It would be good to handle this now so that we >do not have issues in the future.. Do you have any suggestions how this could be handled? <snip> Thanks, Ciara
