# Customize Checking
Override default [checking](../concepts/checking.md) thresholds
for schedulers that tolerate higher imbalance, different gap thresholds,
or relaxed event rates.
## Scheduler-level overrides
Define a `Scheduler` with custom checks:
```rust,ignore
use ktstr::prelude::*;
static MY_LLC: FlagDecl = FlagDecl {
name: "llc",
args: &["--enable-llc"],
requires: &[],
};
static MY_BORROW: FlagDecl = FlagDecl {
name: "borrow",
args: &["--enable-borrowing"],
requires: &[],
};
const RELAXED: Scheduler = Scheduler::new("relaxed")
.binary(SchedulerSpec::Discover("scx_relaxed"))
.flags(&[&MY_LLC, &MY_BORROW])
.assert(
Assert::NO_OVERRIDES
.max_imbalance_ratio(5.0) // tolerate 5:1 imbalance
.max_fallback_rate(500.0) // higher fallback rate ok
.fail_on_stall(false) // don't fail on stall
);
```
These overrides sit between `Assert::default_checks()` and per-test
overrides in the merge chain.
## Per-test overrides via #[ktstr_test]
```rust,ignore
#[ktstr_test(
scheduler = RELAXED_PAYLOAD,
not_starved = true,
max_gap_ms = 5000,
max_imbalance_ratio = 10.0,
sustained_samples = 10,
)]
fn high_imbalance_test(ctx: &Ctx) -> Result<AssertResult> {
// Inherits topology from RELAXED_PAYLOAD
Ok(AssertResult::pass())
}
```
## Understanding not_starved
`not_starved = true` enables starvation, fairness spread, and
scheduling gap checks. Each threshold can be overridden independently.
See [Checking: Worker checks](../concepts/checking.md#worker-checks)
for details and default thresholds.
## Merge order
Three-layer merge with last-`Some`-wins semantics. See
[Checking: Merge layers](../concepts/checking.md#merge-layers).
## Using Assert directly in ops scenarios
```rust,ignore
fn my_scenario(ctx: &Ctx) -> Result<AssertResult> {
let assertions = Assert::NO_OVERRIDES
.check_not_starved()
.max_gap_ms(3000);
let steps = vec![/* ... */];
execute_steps_with(ctx, steps, Some(&assertions))
}
```
`execute_steps_with` applies the given `Assert` for worker checks.
`execute_steps` (without `_with`) passes `None`, falling back to
`ctx.assert` (the merged three-layer config: `default_checks` ->
scheduler -> per-test).
See [Ops and Steps](../concepts/ops.md) for the full step execution
model.