linux-kernel - Re: [PATCH sched_ext/for-6.15] tools/sched_ext: Provide a compatible helper for scx_bpf

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Message-ID: <09bc617e-8360-4aaa-8587-2a2bde1f5ef7@igalia.com>
Date: Thu, 27 Feb 2025 19:27:12 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Andrea Righi <arighi@...dia.com>, Tejun Heo <tj@...nel.org>,
 David Vernet <void@...ifault.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH sched_ext/for-6.15] tools/sched_ext: Provide a compatible
 helper for scx_bpf_events()

Hi Andrea,

On 25. 2. 27. 18:11, Andrea Righi wrote:
> Introduce __COMPAT_scx_bpf_events() to use scx_bpf_events() in a
> compatible way also with kernels that don't provide this kfunc.
> 
> This also fixes the following error with scx_qmap when running on a
> kernel that does not provide scx_bpf_events():
> 
>   ; scx_bpf_events(&events, sizeof(events)); @ scx_qmap.bpf.c:777
>   318: (b7) r2 = 72                     ; R2_w=72 async_cb
>   319: <invalid kfunc call>
>   kfunc 'scx_bpf_events' is referenced but wasn't resolved
> 
> Fixes: 9865f31d852a4 ("sched_ext: Add scx_bpf_events() and scx_read_event() for BPF schedulers")
> Signed-off-by: Andrea Righi <arighi@...dia.com>
> ---
>   tools/sched_ext/include/scx/compat.bpf.h | 8 ++++++++
>   tools/sched_ext/scx_qmap.bpf.c           | 2 +-
>   2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
> index 266f94fe479b7..9252e1a00556f 100644
> --- a/tools/sched_ext/include/scx/compat.bpf.h
> +++ b/tools/sched_ext/include/scx/compat.bpf.h
> @@ -183,7 +183,15 @@ static inline bool __COMPAT_is_enq_cpu_selected(u64 enq_flags)
>   	 bpf_ktime_get_ns())
>   
>   /*
> + * v6.15: Introduce event counters.
>    *
> + * Preserve the following macro until v6.17.
> + */
> +#define __COMPAT_scx_bpf_events(events, size)					\
> +	(bpf_ksym_exists(scx_bpf_events) ?					\
> +	 scx_bpf_events(events, size) : ({}))
> +
> +/*
>    * v6.15: Introduce NUMA-aware kfuncs to operate with per-node idle
>    * cpumasks.
>    *
> diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
> index a6c6be308315a..45fd643d2ca0d 100644
> --- a/tools/sched_ext/scx_qmap.bpf.c
> +++ b/tools/sched_ext/scx_qmap.bpf.c
> @@ -774,7 +774,7 @@ static int monitor_timerfn(void *map, int *key, struct bpf_timer *timer)
>   	if (print_shared_dsq)
>   		dump_shared_dsq();
>   
> -	scx_bpf_events(&events, sizeof(events));
> +	__COMPAT_scx_bpf_events(&events, sizeof(events));
>   
>   	bpf_printk("%35s: %llu", "SCX_EV_SELECT_CPU_FALLBACK",
>   		   scx_read_event(&events, SCX_EV_SELECT_CPU_FALLBACK));

This is a nice catch. Looks good to me.

Thanks!
Changwoo Min