From: "jianchao.wang" <jianchao.w.wang@oracle.com>
To: Keith Busch <keith.busch@intel.com>
Cc: Sagi Grimberg <sagi@grimberg.me>, Christoph Hellwig <hch@lst.de>,
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: Fri, 2 Mar 2018 11:11:22 +0800 [thread overview]
Message-ID: <b2ec4cb3-5125-3fce-4b6d-f483b75d0b2e@oracle.com> (raw)
In-Reply-To: <20180301151544.GA17676@localhost.localdomain>
Hi Keith
Thanks for your kindly directive and precious time for this.
On 03/01/2018 11:15 PM, Keith Busch wrote:
> On Thu, Mar 01, 2018 at 06:05:53PM +0800, jianchao.wang wrote:
>> When the adminq is free, ioq0 irq completion path has to invoke nvme_irq twice, one for itself,
>> one for adminq completion irq action.
>
> Let's be a little more careful on the terminology when referring to spec
> defined features: there is no such thing as "ioq0". The IO queues start
> at 1. The admin queue is the '0' index queue.
Yes, indeed, sorry for my bad description.
>> 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.
>
> Please understand the _overwhelming_ majority of time spent for IRQ
> handling is the context switches. There's a reason you're not able to
> measure a perf difference between IOQ1 and IOQ2: the number of CPU cycles
> to chain a second action is negligible.
>
Yes, indeed
Sincerely
Jianchao
next prev parent reply other threads:[~2018-03-02 3:11 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
2018-03-01 15:15 ` Keith Busch
2018-03-02 3:11 ` jianchao.wang [this message]
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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