On Fri, 13 May 2022 08:50:34 +0200 Heinrich Schuchardt <heinrich.schucha...@canonical.com> wrote:
> On 5/10/22 17:48, Stanislaw Kardach wrote: > > From: Michal Mazurek <m...@semihalf.com> > > > > Add all necessary elements for DPDK to compile and run EAL on SiFive > > Freedom U740 SoC which is based on SiFive U74-MC (ISA: rv64imafdc) > > core complex. > > > > This includes: > > > > - EAL library implementation for rv64imafdc ISA. > > - meson build structure for 'riscv' architecture. RTE_ARCH_RISCV define > > is added for architecture identification. > > - xmm_t structure operation stubs as there is no vector support in the > > U74 core. > > > > Compilation was tested on Ubuntu and Arch Linux using riscv64 toolchain. > > Clang compilation currently not supported due to issues with missing > > relocation relaxation. > > > > Two rte_rdtsc() schemes are provided: stable low-resolution using rdtime > > (default) and unstable high-resolution using rdcycle. User can override > > the scheme by defining RTE_RISCV_RDTSC_USE_HPM=1 during compile time of > > both DPDK and the application. The reasoning for this is as follows. > > The RISC-V ISA mandates that clock read by rdtime has to be of constant > > period and synchronized between all hardware threads within 1 tick > > (chapter 10.1 in version 20191213 of RISC-V spec). > > However this clock may not be of high-enough frequency for dataplane > > uses. I.e. on HiFive Unmatched (FU740) it is 1MHz. > > There is a high-resolution alternative in form of rdcycle which is > > clocked at the core clock frequency. The drawbacks are that it may be > > disabled during sleep (WFI) and its frequency might change due to DVFS. Choosing at compile time is ok for embedded but is undesireable for DPDK in a distribution. It sounds like the low-res is equivalent to hpet and the unstable is same as x86 TSC. Therefore why not follow that precedent and do the same thing?
