1. 11 Jun, 2020 1 commit
    • Vincent Chen's avatar
      riscv: use vDSO common flow to reduce the latency of the time-related functions · ad5d1122
      Vincent Chen authored
      Even if RISC-V has supported the vDSO feature, the latency of the functions
      for obtaining the system time is still expensive. It is because these
      functions still trigger a corresponding system call in the process, which
      slows down the response time. If we want to remove the system call to
      reduce the latency, the kernel should have the ability to output the system
      clock information to userspace. This patch introduces the vDSO common flow
      to enable the kernel to achieve the above feature and uses "rdtime"
      instruction to obtain the current time in the user space. Under this
      condition, the latency cost by the ecall from U-mode to S-mode can be
      eliminated. After applying this patch, the latency of gettimeofday()
      measured on the HiFive unleashed board can be reduced by %61.
      Signed-off-by: default avatarVincent Chen <vincent.chen@sifive.com>
      Reviewed-by: default avatarAtish Patra <atish.patra@wdc.com>
      Signed-off-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
      ad5d1122
  2. 10 Jun, 2020 9 commits
  3. 05 Jun, 2020 30 commits