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  • 1 commit
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Commits on Feb 29, 2024

  1. unscaledcycleclock: use RDTIME instead of RDCYCLE on RISC-V 

    Starting with Linux 6.6 [1], RDCYCLE is a privileged instruction on
RISC-V and can't be used directly from userland. There is a sysctl
option to change that as a transition period, but it will eventually
disappear.

Use RDTIME instead, which while less accurate has the advantage of being
synchronized between CPU (and thus monotonic) and of constant frequency.
Therefore this change also fixes another issue caused by wrong time
measurement when a process is rescheduled from one CPU to another [2].

Given RDTIME uses a timer independent from the CPU, this patche removes
the ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY define
accordingly.

This fixes the testsuite on riscv64, tested on a VisionFive 2 board.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cc4c07c89aada16229084eeb93895c95b7eabaa3
[2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1025221
    @aurel32
    aurel32 committed Feb 29, 2024
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