linux-kernel - Re: [PATCH v3 4/5] genirq/affinity: allow driver's discontigous affinity set

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Message-ID: <20190625021411.GD23777@ming.t460p>
Date:   Tue, 25 Jun 2019 10:14:12 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Weiping Zhang <zhangweiping@...iglobal.com>, axboe@...nel.dk,
        Tejun Heo <tj@...nel.org>, Christoph Hellwig <hch@....de>,
        bvanassche@....org, keith.busch@...el.com, minwoo.im.dev@...il.com,
        linux-block@...r.kernel.org, cgroups@...r.kernel.org,
        linux-nvme@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/5] genirq/affinity: allow driver's discontigous
 affinity set

Hi Thomas,

On Mon, Jun 24, 2019 at 05:42:39PM +0200, Thomas Gleixner wrote:
> On Mon, 24 Jun 2019, Weiping Zhang wrote:
> 
> > The driver may implement multiple affinity set, and some of
> > are empty, for this case we just skip them.
> 
> Why? What's the point of creating empty sets? Just because is not a real
> good justification.

Patch 5 will add 4 new sets for supporting NVMe's weighted round robin
arbitration. It can be a headache to manage so many irq sets(now the total
sets can become 6) dynamically since size of anyone in the new 4 sets can
be zero, so each particular set is assigned one static index for avoiding
the management trouble, then empty set will be seen by
irq_create_affinity_masks().

So looks skipping the empty set makes sense because the API will become
easier to use than before.

Thanks,
Ming