On Thu, Sep 11, 2025 at 02:58:22PM -0700, Ankur Arora wrote: > > Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> writes: > > > On Thu, 11 Sept 2025 at 16:32, Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > >> > >> On Wed, Sep 10, 2025 at 08:46:55PM -0700, Ankur Arora wrote: > >> > Switch out the conditional load inerfaces used by rqspinlock > >> > to smp_cond_read_acquire_timeout(). > >> > This interface handles the timeout check explicitly and does any > >> > necessary amortization, so use check_timeout() directly. > >> > >> It's worth mentioning that the default smp_cond_load_acquire_timeout() > >> implementation (without hardware support) only spins 200 times instead > >> of 16K times in the rqspinlock code. That's probably fine but it would > >> be good to have confirmation from Kumar or Alexei. > >> > > > > This looks good, but I would still redefine the spin count from 200 to > > 16k for rqspinlock.c, especially because we need to keep > > RES_CHECK_TIMEOUT around which still uses 16k spins to amortize > > check_timeout. > > By my count that amounts to ~100us per check_timeout() on x86 > systems I've tested with cpu_relax(). Which seems quite reasonable. > > 16k also seems safer on CPUs where cpu_relax() is basically a NOP. Does this spin count work for poll_idle()? I don't remember where the 200 value came from. -- Catalin
