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