Forwarded: https://github.com/MariaDB/server/pull/2980 Origin: https://patch-diff.githubusercontent.com/raw/MariaDB/server/pull/2980.patch From: Aurelien Jarno Date: Thu, 4 Jan 2024 11:30:34 +0100 Subject: [PATCH] RISC-V: use RDTIME instead of RDCYCLE 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. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cc4c07c89aada16229084eeb93895c95b7eabaa3 --- include/my_rdtsc.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) --- a/include/my_rdtsc.h +++ b/include/my_rdtsc.h @@ -111,7 +111,7 @@ C_MODE_START On AARCH64, we use the generic timer base register. We override clang implementation for aarch64 as it access a PMU register which is not guaranteed to be active. - On RISC-V, we use the rdcycle instruction to read from mcycle register. + On RISC-V, we use the rdtime instruction to read from mtime register. Sadly, we have nothing for the Digital Alpha, MIPS, Motorola m68k, HP PA-RISC or other non-mainstream (or obsolete) processors. @@ -211,15 +211,15 @@ static inline ulonglong my_timer_cycles( } #elif defined(__riscv) #define MY_TIMER_ROUTINE_CYCLES MY_TIMER_ROUTINE_RISCV - /* Use RDCYCLE (and RDCYCLEH on riscv32) */ + /* Use RDTIME (and RDTIMEH on riscv32) */ { # if __riscv_xlen == 32 ulong result_lo, result_hi0, result_hi1; /* Implemented in assembly because Clang insisted on branching. */ __asm __volatile__( - "rdcycleh %0\n" - "rdcycle %1\n" - "rdcycleh %2\n" + "rdtimeh %0\n" + "rdtime %1\n" + "rdtimeh %2\n" "sub %0, %0, %2\n" "seqz %0, %0\n" "sub %0, zero, %0\n" @@ -228,7 +228,7 @@ static inline ulonglong my_timer_cycles( return (static_cast(result_hi1) << 32) | result_lo; # else ulonglong result; - __asm __volatile__("rdcycle %0" : "=r"(result)); + __asm __volatile__("rdtime %0" : "=r"(result)); return result; } # endif