Help¶

Qemu (without -icount) has trouble keeping time when the host process needs to timeshare. The host OS will routinely schedule out a process at timescales equivalent to the guest tick rate. With traditional ticks delivered regularly by the hardware, that’s mostly OK as it looks like a late interrupt. But in tickless mode, the driver needs some CPU in order to schedule the tick in the first place. If that gets delayed across a tick boundary, time gets wonky. This tunable is a hint to the driver to disable tickless accounting on qemu. Use it only on tests that are known to have problems.

Direct dependencies¶

QEMU_TARGET && TICKLESS_KERNEL

(Includes any dependencies from ifs and menus.)

Defaults¶

No defaults. Implicitly defaults to n.

Kconfig definition¶

At drivers/timer/Kconfig:287

Included via Kconfig:8 → Kconfig.zephyr:40 → drivers/Kconfig:24

Menu path: (Top) → Device Drivers → Timer Drivers

config QEMU_TICKLESS_WORKAROUND
    bool "Disable tickless on qemu due to asynchrony bug"
    depends on QEMU_TARGET && TICKLESS_KERNEL
    help
      Qemu (without -icount) has trouble keeping time when the
      host process needs to timeshare.  The host OS will routinely
      schedule out a process at timescales equivalent to the guest
      tick rate.  With traditional ticks delivered regularly by
      the hardware, that's mostly OK as it looks like a late
      interrupt.  But in tickless mode, the driver needs some CPU
      in order to schedule the tick in the first place.  If that
      gets delayed across a tick boundary, time gets wonky.  This
      tunable is a hint to the driver to disable tickless
      accounting on qemu.  Use it only on tests that are known to
      have problems.

(The ‘depends on’ condition includes propagated dependencies from ifs and menus.)