From: Keith Busch <kbusch@kernel.org>
To: "Nadolski, Edmund" <edmund.nadolski@intel.com>
Cc: hch@lst.de, linux-nvme@lists.infradead.org, sagi@grimberg.me
Subject: Re: [PATCH] nvme/pci: Remove last_sq_tail
Date: Fri, 6 Dec 2019 05:48:12 +0900 [thread overview]
Message-ID: <20191205204812.GA27699@redsun51.ssa.fujisawa.hgst.com> (raw)
In-Reply-To: <149bb39b-e8ab-36a5-f319-18ef5e3567b6@intel.com>
On Thu, Dec 05, 2019 at 01:31:20PM -0700, Nadolski, Edmund wrote:
> On 12/5/2019 1:08 PM, Keith Busch wrote:
> > We don't allocate enough tags to wrap the submission queue. Remove
> > tracking for this condition.
>
> Can we ensure that this presumption won't change?
If we did have more tags, there'd be no guarantee we could even dispatch
them, and we'd have to track the CQE sq_head value to ensure an available
slot. There's really no performance win to adding that overhead to the
driver. On top of that, I'm aware there are more than a few controllers
that will break if we wrap the submission queue. So I don't see this
changing.
> > @@ -462,21 +461,11 @@ static int nvme_pci_map_queues(struct blk_mq_tag_set *set)
> > /*
> > * Write sq tail if we are asked to, or if the next command would wrap.
>
> Comment needs to be updated.
Yep, that comment would be outdated with this patch.
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next prev parent reply other threads:[~2019-12-05 20:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-05 20:08 [PATCH] nvme/pci: Remove last_sq_tail Keith Busch
2019-12-05 20:31 ` Nadolski, Edmund
2019-12-05 20:48 ` Keith Busch [this message]
2019-12-12 9:20 ` Christoph Hellwig
2019-12-12 15:47 ` Keith Busch
2019-12-12 20:11 ` Sagi Grimberg
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