linux-kernel - Re: [PATCH v5 4/6] sched_ext: Add time helpers for BPF schedulers

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Message-ID: <Z1_Yh7V_4EEXswkY@gpd3>
Date: Mon, 16 Dec 2024 08:36:39 +0100
From: Andrea Righi <arighi@...dia.com>
To: Changwoo Min <multics69@...il.com>
Cc: tj@...nel.org, void@...ifault.com, mingo@...hat.com,
	peterz@...radead.org, kernel-dev@...lia.com,
	linux-kernel@...r.kernel.org, Changwoo Min <changwoo@...lia.com>
Subject: Re: [PATCH v5 4/6] sched_ext: Add time helpers for BPF schedulers

Hi Changwoo,

On Mon, Dec 16, 2024 at 12:11:42PM +0900, Changwoo Min wrote:
> The following functions are added for BPF schedulers:
> - vtime_delta(after, before)
> - vtime_after(a, b)
> - vtime_before(a, b)
> - vtime_after_eq(a, b)
> - vtime_before_eq(a, b)
> - vtime_in_range(a, b, c)
> - vtime_in_range_open(a, b, c)

Considering that we sync these headers and sched examples from the scx repo
(see https://github.com/sched-ext/scx/blob/main/scheds/sync-to-kernel.sh),
maybe we could have a corresponding change there as well and include a link
to the PR here (as "Link: ...").

Moreover, tis particular change doesn't require to have the rest of the
patch set applied to the kernel, so a PR can be created even now. In this
way we don't risk to get out of sync.

What do you think?

Thanks,
-Andrea

> 
> Signed-off-by: Changwoo Min <changwoo@...lia.com>
> ---
>  tools/sched_ext/include/scx/common.bpf.h | 94 ++++++++++++++++++++++++
>  1 file changed, 94 insertions(+)
> 
> diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
> index 79f0798a5350..923bbf57e4f1 100644
> --- a/tools/sched_ext/include/scx/common.bpf.h
> +++ b/tools/sched_ext/include/scx/common.bpf.h
> @@ -408,6 +408,100 @@ static __always_inline const struct cpumask *cast_mask(struct bpf_cpumask *mask)
>  void bpf_rcu_read_lock(void) __ksym;
>  void bpf_rcu_read_unlock(void) __ksym;
>  
> +/*
> + * Time helpers, most of which are from jiffies.h.
> + */
> +
> +/**
> + * vtime_delta - Calculate the delta between new and old time stamp
> + * @after: first comparable as u64
> + * @before: second comparable as u64
> + *
> + * Return: the time difference, which is >= 0
> + */
> +static inline s64 vtime_delta(u64 after, u64 before)
> +{
> +	return (s64)(after - before) > 0 ? : 0;
> +}
> +
> +/**
> + * vtime_after - returns true if the time a is after time b.
> + * @a: first comparable as u64
> + * @b: second comparable as u64
> + *
> + * Do this with "<0" and ">=0" to only test the sign of the result. A
> + * good compiler would generate better code (and a really good compiler
> + * wouldn't care). Gcc is currently neither.
> + *
> + * Return: %true is time a is after time b, otherwise %false.
> + */
> +static inline bool vtime_after(u64 a, u64 b)
> +{
> +	 return (s64)(b - a) < 0;
> +}
> +
> +/**
> + * vtime_before - returns true if the time a is before time b.
> + * @a: first comparable as u64
> + * @b: second comparable as u64
> + *
> + * Return: %true is time a is before time b, otherwise %false.
> + */
> +static inline bool vtime_before(u64 a, u64 b)
> +{
> +	return vtime_after(b, a);
> +}
> +
> +/**
> + * vtime_after_eq - returns true if the time a is after or the same as time b.
> + * @a: first comparable as u64
> + * @b: second comparable as u64
> + *
> + * Return: %true is time a is after or the same as time b, otherwise %false.
> + */
> +static inline bool vtime_after_eq(u64 a, u64 b)
> +{
> +	 return (s64)(a - b) >= 0;
> +}
> +
> +/**
> + * vtime_before_eq - returns true if the time a is before or the same as time b.
> + * @a: first comparable as u64
> + * @b: second comparable as u64
> + *
> + * Return: %true is time a is before or the same as time b, otherwise %false.
> + */
> +static inline bool vtime_before_eq(u64 a, u64 b)
> +{
> +	return vtime_after_eq(b, a);
> +}
> +
> +/**
> + * vtime_in_range - Calculate whether a is in the range of [b, c].
> + * @a: time to test
> + * @b: beginning of the range
> + * @c: end of the range
> + *
> + * Return: %true is time a is in the range [b, c], otherwise %false.
> + */
> +static inline bool vtime_in_range(u64 a, u64 b, u64 c)
> +{
> +	return vtime_after_eq(a, b) && vtime_before_eq(a, c);
> +}
> +
> +/**
> + * vtime_in_range_open - Calculate whether a is in the range of [b, c).
> + * @a: time to test
> + * @b: beginning of the range
> + * @c: end of the range
> + *
> + * Return: %true is time a is in the range [b, c), otherwise %false.
> + */
> +static inline bool vtime_in_range_open(u64 a, u64 b, u64 c)
> +{
> +	return vtime_after_eq(a, b) && vtime_before(a, c);
> +}
> +
>  
>  /*
>   * Other helpers
> -- 
> 2.47.1
>