linux-kernel - Re: [PATCH v2] nvme-pci: Support shared tags across queues for Apple 2018 controllers

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Message-ID: <448cfd6b3e798dfbef45fa72e0819b1cb39cf68d.camel@kernel.crashing.org>
Date:   Fri, 19 Jul 2019 15:15:14 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Damien Le Moal <Damien.LeMoal@....com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Pawlowski <paul@...rm.io>, Jens Axboe <axboe@...com>,
        Minwoo Im <minwoo.im.dev@...il.com>,
        Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2] nvme-pci: Support shared tags across queues for
 Apple 2018 controllers

On Fri, 2019-07-19 at 05:01 +0000, Damien Le Moal wrote:
> > I suppose that would work and be simpler. I honestly don't know much
> > about the block layer and tag allocation so I stayed away from it :-)
> > 
> > I'll dig, but a hint would be welcome :)
> 
> Uuuh.. Never played with the tag management code directly myself either. A quick
> look seem to indicate that blk_mq_get/put_tag() is what you should be using. But
> further looking, struct blk_mq_tags has the field nr_reserved_tags which is used
> as an offset start point for searching free tags, which is exactly what you
> would need.

Yup. I was getting there, it's just that we use the tagset mess which I
had to untangle a bit first :-)

Cheers,
Ben.