On Fri, Jul 21, 2023 at 04:08:10PM +0100, Valentin Schneider wrote: > 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. Agreed. If a need for variable numbers of bits ever does arise, we can worry about it at that time. And then we would have more information on what a variable-bit facility should look like. Thanx, Paul
