linux-kernel - Re: [patch v6 7/7] genirq/affinity: Add support for non-managed affinity sets

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Message-ID: <alpine.DEB.2.21.1902180824070.1683@nanos.tec.linutronix.de>
Date:   Mon, 18 Feb 2019 08:25:49 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ming Lei <ming.lei@...hat.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-pci@...r.kernel.org,
        Keith Busch <keith.busch@...el.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Shivasharan Srikanteshwara 
        <shivasharan.srikanteshwara@...adcom.com>
Subject: Re: [patch v6 7/7] genirq/affinity: Add support for non-managed
 affinity sets

Ming,

On Mon, 18 Feb 2019, Ming Lei wrote:
> On Sun, Feb 17, 2019 at 08:17:05PM +0100, Thomas Gleixner wrote:
> > I don't see how that would break blk-mq. The unmanaged set is not used by
> > the blk-mq stuff, that's some driver internal voodoo. So blk-mq still gets
> > a perfectly spread and managed interrupt set for the queues.
> 
> >From the discussion above, the use case is for megaraid_sas. And one of the
> two interrupt sets(managed and non-managed) will be chosen according to
> workloads runtime.
> 
> Each interrupt set actually defines one blk-mq queue mapping, and the
> queue mapping needs to respect the rule I mentioned now. However,
> non-managed affinity can be changed to any way anytime by user-space.
> 
> Recently HPSA tried to add one module parameter to use non-managed
> IRQ[1].
> 
> Also NVMe RDMA uses non-managed interrupts, and at least one CPU hotplug
> issue is never fixed yet[2]. 
> 
> [1] https://marc.info/?t=154387665200001&r=1&w=2
> [2] https://www.spinics.net/lists/linux-block/msg24140.html

Interesting. I misread the description which megasas folks provided
then. I'll drop that patch and get the other lot merged. Thanks for your
work and help with that!

Thanks,

	tglx