From: "jianchao.wang" <jianchao.w.wang@oracle.com>
To: Sagi Grimberg <sagi@grimberg.me>, Christoph Hellwig <hch@lst.de>
Cc: keith.busch@intel.com, axboe@fb.com,
linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org
Subject: Re: [PATCH V2] nvme-pci: assign separate irq vectors for adminq and ioq0
Date: Thu, 1 Mar 2018 18:05:53 +0800 [thread overview]
Message-ID: <66e4ad3e-4019-13ec-94c0-e168cc1d95b4@oracle.com> (raw)
In-Reply-To: <ddfc2ab4-1a51-c488-25e8-bc434edf8aba@grimberg.me>
Hi sagi
Thanks for your kindly response.
On 03/01/2018 05:28 PM, Sagi Grimberg wrote:
>
>> Note that we originally allocates irqs this way, and Keith changed
>> it a while ago for good reasons. So I'd really like to see good
>> reasons for moving away from this, and some heuristics to figure
>> out which way to use. E.g. if the device supports more irqs than
>> I/O queues your scheme might always be fine.
>
> I still don't understand what this buys us in practice. Seems redundant
> to allocate another vector without any (even marginal) difference.
>
When the adminq is free, ioq0 irq completion path has to invoke nvme_irq twice, one for itself,
one for adminq completion irq action.
We are trying to save every cpu cycle across the nvme host path, why we waste nvme_irq cycles here.
If we have enough vectors, we could allocate another irq vector for adminq to avoid this.
Sincerely
Jianchao
next prev parent reply other threads:[~2018-03-01 10:06 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-28 15:48 [PATCH V2] nvme-pci: assign separate irq vectors for adminq and ioq0 Jianchao Wang
2018-02-28 15:59 ` Andy Shevchenko
2018-03-02 3:06 ` jianchao.wang
2018-03-12 18:59 ` Keith Busch
2018-03-13 1:47 ` jianchao.wang
2018-02-28 16:47 ` Christoph Hellwig
2018-03-01 9:28 ` Sagi Grimberg
2018-03-01 10:05 ` jianchao.wang [this message]
2018-03-01 15:15 ` Keith Busch
2018-03-02 3:11 ` jianchao.wang
2018-03-01 15:03 ` Ming Lei
2018-03-01 16:10 ` Keith Busch
2018-03-08 7:42 ` Christoph Hellwig
2018-03-09 17:24 ` Keith Busch
2018-03-12 9:09 ` Ming Lei
2018-03-02 3:18 ` jianchao.wang
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