linux-kernel - Re: [PATCH 2/4] sched_ext: Get rid of the scx_selcpu_topo

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Message-ID: <f6cdf7d9-b11a-4b6b-9d30-35afb50a55f1@igalia.com>
Date: Wed, 11 Dec 2024 17:05:35 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Andrea Righi <arighi@...dia.com>, Tejun Heo <tj@...nel.org>,
 David Vernet <void@...ifault.com>
Cc: Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] sched_ext: Get rid of the scx_selcpu_topo_numa logic

Hello Andrea,

On 24. 12. 9. 19:40, Andrea Righi wrote:
>   /*
> @@ -3519,9 +3476,8 @@ static void update_selcpu_topology(void)
>    * 4. Pick a CPU within the same NUMA node, if enabled:
>    *   - choose a CPU from the same NUMA node to reduce memory access latency.
>    *
> - * Step 3 and 4 are performed only if the system has, respectively, multiple
> - * LLC domains / multiple NUMA nodes (see scx_selcpu_topo_llc and
> - * scx_selcpu_topo_numa).
> + * Step 3 is performed only if the system has multiple LLC domains that are not
> + * perfectly overlapping with the NUMA domains (see scx_selcpu_topo_llc).
>    *
>    * NOTE: tasks that can only run on 1 CPU are excluded by this logic, because
>    * we never call ops.select_cpu() for them, see select_task_rq().
> @@ -3530,7 +3486,6 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>   			      u64 wake_flags, bool *found)


Adding Step 5 to the comment describing how it works if there is no idle 
CPU within a NUMA node would be nice. For example,

   5. Pick any idle CPU usable by the task.

Regards,
Changwoo Min