RE: [PATCH 1/2] wifi: rtlwifi: add WQ_PERCPU to alloc_workqueue users

[Ping-Ke Shih]

Marco Crivellari <marco.crivellari@xxxxxxxx> wrote:
> Currently if a user enqueues a work item using schedule_delayed_work() the
> used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
> WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
> schedule_work() that is using system_wq and queue_work(), that makes use
> again of WORK_CPU_UNBOUND.
> 
> This lack of consistency cannot be addressed without refactoring the API.
> For more details see the Link tag below.
> 
> alloc_workqueue() treats all queues as per-CPU by default, while unbound
> workqueues must opt-in via WQ_UNBOUND.
> 
> This default is suboptimal: most workloads benefit from unbound queues,
> allowing the scheduler to place worker threads where they’re needed and
> reducing noise when CPUs are isolated.
> 
> This continues the effort to refactor workqueue APIs, which began with
> the introduction of new workqueues and a new alloc_workqueue flag in:
> 
> commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
> 
> This change adds a new WQ_PERCPU flag to explicitly request
> alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.
> 
> With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
> any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
> must now use WQ_PERCPU.
> 
> Once migration is complete, WQ_UNBOUND can be removed and unbound will
> become the implicit default.
> 
> Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
> Signed-off-by: Marco Crivellari <marco.crivellari@xxxxxxxx>
> Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@xxxxxxxxxxxxx/
> ---
>  drivers/net/wireless/realtek/rtlwifi/base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/realtek/rtlwifi/base.c b/drivers/net/wireless/realtek/rtlwifi/base.c
> index e26feb8de658..2786e4ee67eb 100644
> --- a/drivers/net/wireless/realtek/rtlwifi/base.c
> +++ b/drivers/net/wireless/realtek/rtlwifi/base.c
> @@ -445,7 +445,7 @@ static int _rtl_init_deferred_work(struct ieee80211_hw *hw)
>         struct rtl_priv *rtlpriv = rtl_priv(hw);
>         struct workqueue_struct *wq;
> 
> -       wq = alloc_workqueue("%s", 0, 0, rtlpriv->cfg->name);
> +       wq = alloc_workqueue("%s", WQ_PERCPU, 0, rtlpriv->cfg->name);

I think this driver should use WQ_UNBOUND as well as another patch in this
patchset. 


I feel most user scenarios should be WQ_UNBOUND. Could you share which case
uses WQ_PERCPU?


>         if (!wq)
>                 return -ENOMEM;
> 
> --
> 2.51.1