linux-kernel - Re: [PATCH net-next 08/11] net: hns3: add interrupt affinity support for misc interrupt

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Date:   Fri, 26 Jul 2019 23:18:48 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "linyunsheng@...wei.com" <linyunsheng@...wei.com>,
        "tanhuazhong@...wei.com" <tanhuazhong@...wei.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "lipeng321@...wei.com" <lipeng321@...wei.com>,
        "yisen.zhuang@...wei.com" <yisen.zhuang@...wei.com>,
        "salil.mehta@...wei.com" <salil.mehta@...wei.com>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 08/11] net: hns3: add interrupt affinity support
 for misc interrupt

On Thu, 2019-07-25 at 10:05 +0800, Yunsheng Lin wrote:
> On 2019/7/25 3:24, Saeed Mahameed wrote:
> > On Wed, 2019-07-24 at 11:18 +0800, Huazhong Tan wrote:
> > > From: Yunsheng Lin <linyunsheng@...wei.com>
> > > 

[...]
> > > 
> > > +static void hclge_irq_affinity_notify(struct irq_affinity_notify
> > > *notify,
> > > +				      const cpumask_t *mask)
> > > +{
> > > +	struct hclge_dev *hdev = container_of(notify, struct hclge_dev,
> > > +					      affinity_notify);
> > > +
> > > +	cpumask_copy(&hdev->affinity_mask, mask);
> > > +	del_timer_sync(&hdev->service_timer);
> > > +	hdev->service_timer.expires = jiffies + HZ;
> > > +	add_timer_on(&hdev->service_timer, cpumask_first(&hdev-
> > > > affinity_mask));
> > > +}
> > 
> > I don't see any relation between your misc irq vector and &hdev-
> > > service_timer, to me this looks like an abuse of the irq affinity
> > > API
> > to allow the user to move the service timer affinity.
> 
> Hi, thanks for reviewing.
> 
> hdev->service_timer is used to schedule the periodic work
> queue hdev->service_task， we want all the management work
> queue including hdev->service_task to bind to the same cpu
> to improve cache and power efficiency, it is better to move
> service timer affinity according to that.
> 
> The hdev->service_task is changed to delay work queue in
> next patch " net: hns3: make hclge_service use delayed workqueue",
> So the affinity in the timer of the delay work queue is automatically
> set to the affinity of the delay work queue, we will move the
> "make hclge_service use delayed workqueue" patch before the
> "add interrupt affinity support for misc interrupt" patch, so
> we do not have to set service timer affinity explicitly.
> 
> Also, There is there work queues(mbx_service_task, service_task,
> rst_service_task) in the hns3 driver, we plan to combine them
> to one or two workqueue to improve efficiency and readability.
> 

So just to make it clear, you have 3 deferred works, 2 are triggered by
the misc irq and 1 is periodic, you want them all on the same core and
you want to control their affinity via the irq affinity ? for works #1
and  #2 you get that for free since the irq is triggering them, but for
work #3 (the periodic one) you need to manually move it when the irq
affinity changes.

I guess i am ok with this, since moving the irq affinity isn't only
required by the periodic work but also for the other works that the irq
is actually triggering (so it is not an actual abuse, sort of .. )