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Subject: Re: [PATCH 3/3] brcmfmac: make setting SDIO workqueue WQ_HIGHPRI a
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To:     Tejun Heo <tj@kernel.org>
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From:   Wright Feng <wright.feng@cypress.com>
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Date:   Wed, 25 Mar 2020 12:29:44 +0800
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Tejun Heo 於 3/25/2020 2:23 AM 寫道:
> Hello,
> 
> On Fri, Mar 20, 2020 at 04:08:47PM +0800, Wright Feng wrote:
>>> So two things changed, 1) WQ_HIGHPRI flag added *and* 2) use
>>> allow_workqueue basically dropping __WQ_ORDERED. Not sure which one
>>> contributes to the behavior described in the commit message.
>>
>> The combination of Unbound and max_active==1 implies ordered, so I suppose
>> we don't need to set __WQ_ORDERED bit in flags.
> 
> It doesn't on NUMA setups. If you need ordered execution, you need the flag.
> 
> Thanks.
>
Hi Tejun,
In kernel/workqueue.c, it helps set __WQ_ORDERED flag for the 
condition(Unbound && max_active == 1) to keep the previous behavior to 
avoid subtle breakages on NUMA.
Does it mean we don't have to set the flags in alloc_workqueue? or I 
misunderstand something?
If that's incorrect, would you please give me a hint how to set 
__WQ_ORDERED(internal use flag) and WQ_HIGHPRI flags at the same time?

---
/*
  * Unbound && max_active == 1 used to imply ordered, which is no
  * longer the case on NUMA machines due to per-node pools.  While
  * alloc_ordered_workqueue() is the right way to create an ordered
  * workqueue, keep the previous behavior to avoid subtle breakages
  * on NUMA.
  */
if ((flags & WQ_UNBOUND) && max_active == 1)
     flags |= __WQ_ORDERED;
---

Regards,
Wright