linux-kernel - Re: [PATCH v2 1/4] sched/isolation: API to get housekeeping online CPUs

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Date:   Thu, 24 Sep 2020 08:23:29 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Frederic Weisbecker <frederic@...nel.org>, peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-pci@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        mtosatti@...hat.com, sassmann@...hat.com,
        jesse.brandeburg@...el.com, lihong.yang@...el.com,
        helgaas@...nel.org, jeffrey.t.kirsher@...el.com,
        jacob.e.keller@...el.com, jlelli@...hat.com, hch@...radead.org,
        bhelgaas@...gle.com, mike.marciniszyn@...el.com,
        dennis.dalessandro@...el.com, thomas.lendacky@....com,
        jerinj@...vell.com, mathias.nyman@...el.com, jiri@...dia.com,
        mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org
Subject: Re: [PATCH v2 1/4] sched/isolation: API to get housekeeping online
 CPUs


On 9/24/20 8:09 AM, Frederic Weisbecker wrote:
> On Thu, Sep 24, 2020 at 10:40:29AM +0200, peterz@...radead.org wrote:
>> On Wed, Sep 23, 2020 at 02:11:23PM -0400, Nitesh Narayan Lal wrote:
>>> Introduce a new API hk_num_online_cpus(), that can be used to
>>> retrieve the number of online housekeeping CPUs that are meant to handle
>>> managed IRQ jobs.
>>>
>>> This API is introduced for the drivers that were previously relying only
>>> on num_online_cpus() to determine the number of MSIX vectors to create.
>>> In an RT environment with large isolated but fewer housekeeping CPUs this
>>> was leading to a situation where an attempt to move all of the vectors
>>> corresponding to isolated CPUs to housekeeping CPUs were failing due to
>>> per CPU vector limit.
>>>
>>> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
>>> ---
>>>  include/linux/sched/isolation.h | 13 +++++++++++++
>>>  1 file changed, 13 insertions(+)
>>>
>>> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
>>> index cc9f393e2a70..2e96b626e02e 100644
>>> --- a/include/linux/sched/isolation.h
>>> +++ b/include/linux/sched/isolation.h
>>> @@ -57,4 +57,17 @@ static inline bool housekeeping_cpu(int cpu, enum hk_flags flags)
>>>  	return true;
>>>  }
>>>  
>>> +static inline unsigned int hk_num_online_cpus(void)
>> This breaks with the established naming of that header.
> I guess we can make it housekeeping_num_online_cpus() ?

Right, I can do that.

Thanks

>
-- 
Nitesh



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