linux-kernel - Re: [PATCH v2 01/11] genirq/affinity:: Export irq_create_affinity

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Message-ID: <20230213065116-mutt-send-email-mst@kernel.org>
Date:   Mon, 13 Feb 2023 06:59:39 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Yongji Xie <xieyongji@...edance.com>
Cc:     Christoph Hellwig <hch@....de>, Jason Wang <jasowang@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 01/11] genirq/affinity:: Export
 irq_create_affinity_masks()

On Mon, Jan 30, 2023 at 07:53:55PM +0800, Yongji Xie wrote:
> On Fri, Jan 27, 2023 at 4:22 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > On Mon, Dec 19, 2022 at 05:36:02PM +0800, Yongji Xie wrote:
> > > On Mon, Dec 19, 2022 at 3:33 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > > >
> > > > On Mon, Dec 05, 2022 at 04:41:17PM +0800, Xie Yongji wrote:
> > > > > Export irq_create_affinity_masks() so that some modules
> > > > > can make use of it to implement interrupt affinity
> > > > > spreading mechanism.
> > > > >
> > > > > Signed-off-by: Xie Yongji <xieyongji@...edance.com>
> > > >
> > > > So this got nacked, what's the plan now?
> > > >
> > >
> > > I‘d like to check with Christoph again first.
> > >
> > > Hi Christoph,
> > >
> > > Jason will post some patches to get rid of the DMA API for vDPA
> > > simulators. And the irq affinity algorithm is independent of the IRQ
> > > subsystem IIUC. So could you allow this patch so that we can reuse the
> > > algorithm to select the best CPU (per-cpu affinity if possible, or at
> > > least per-node) to run the virtqueue's irq callback.
> > >
> > > Thanks,
> > > Yongji
> >
> > I think you need to explain why you are building low level
> > affinity masks.
> 
> In VDUSE case, we use workqueue to run the virtqueue's irq callback.
> Now I want to queue the irq callback kwork to one specific CPU to get
> per-cpu affinity if possible, or at least per-node. So I need to use
> this function to build the low level affinity masks for each
> virtqueue.
> 
> > what's the plan now?
> >
> 
> If there is no objection, I'll post a new version.
> 
> Thanks,
> Yongji

I doubt you made a convicing case here - I think Christoph was saying if
it is not an irq it should not use an irq affinity API.
So a new API possibly sharing implementation with irq affinity
is called for then? Maybe.


-- 
MST