On 21/07/23 07:10, Paul E. McKenney wrote: > On Fri, Jul 21, 2023 at 09:17:53AM +0100, Valentin Schneider wrote: >> On 20/07/23 17:30, Valentin Schneider wrote: >> > index bdd7eadb33d8f..1ff2aab24e964 100644 >> > --- a/kernel/rcu/Kconfig >> > +++ b/kernel/rcu/Kconfig >> > @@ -332,4 +332,37 @@ config RCU_DOUBLE_CHECK_CB_TIME >> > Say Y here if you need tighter callback-limit enforcement. >> > Say N here if you are unsure. >> > >> > +config RCU_DYNTICKS_RANGE_BEGIN >> > + int >> > + depends on !RCU_EXPERT >> > + default 31 if !CONTEXT_TRACKING_WORK >> >> You'll note that this should be 30 really, because the lower *2* bits are >> taken by the context state (CONTEXT_GUEST has a value of 3). >> >> This highlights the fragile part of this: the Kconfig values are hardcoded, >> but they depend on CT_STATE_SIZE, CONTEXT_MASK and CONTEXT_WORK_MAX. The >> static_assert() will at least capture any misconfiguration, but having that >> enforced by the actual Kconfig ranges would be less awkward. >> >> Do we currently have a way of e.g. making a Kconfig file depend on and use >> values generated by a C header? > > Why not just have something like a boolean RCU_DYNTICKS_TORTURE Kconfig > option and let the C code work out what the number of bits should be? > > I suppose that there might be a failure whose frequency depended on > the number of bits, which might be an argument for keeping something > like RCU_DYNTICKS_RANGE_BEGIN for fault isolation. But still using > RCU_DYNTICKS_TORTURE for normal testing. > > Thoughts? > AFAICT if we run tests with the minimum possible width, then intermediate values shouldn't have much value. Your RCU_DYNTICKS_TORTURE suggestion sounds like a saner option than what I came up with, as we can let the context tracking code figure out the widths itself and not expose any of that to Kconfig. > Thanx, Paul
