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From: Hannes Reinecke <hare@suse.de>
To: Keith Busch <kbusch@kernel.org>
Cc: Sagi Grimberg <sagi@grimberg.me>, Long Li <longli@microsoft.com>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@fb.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue
Date: Tue, 12 Nov 2019 18:29:34 +0100
Message-ID: <f69d4e4c-3d6e-74c0-ed97-cac3c6b230c2@suse.de> (raw)
In-Reply-To: <20191112164947.GB29135@redsun51.ssa.fujisawa.hgst.com>

On 11/12/19 5:49 PM, Keith Busch wrote:
> On Tue, Nov 12, 2019 at 05:25:59PM +0100, Hannes Reinecke wrote:
>> (Nitpick: what does happen with the interrupt if we have a mask of
>> several CPUs? Will the interrupt delivered to one CPU?
>> To all in the mask?
> 
> The hard-interrupt will be delivered to effectively one of the CPUs in the
> mask. The one that is selected is determined when the IRQ is allocated,
> and it should try to select one form the mask that is least used (see
> matrix_find_best_cpu_managed()).
> 
Yeah, just as I thought.
Which also means that we need to redirect the irq to a non-busy cpu to 
avoid stalls under high load.
Expecially if we have several NVMes to deal with.

>> Can't we implement blk_poll? Or maybe even threaded interrupts?
> 
> Threaded interrupts sound good. Currently, though, threaded interrupts
> execute only on the same cpu as the hard irq. There was a proposal here to
> change that to use any CPU in the mask, and I still think it makes sense
> 
>    http://lists.infradead.org/pipermail/linux-nvme/2019-August/026628.html
> 
That looks like just the ticket.
In combination with threaded irqs and possibly blk_poll to avoid irq 
storms we should be good.

Let's see if I can come up with something...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@suse.de                              +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)

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Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-08  3:55 [PATCH 0/2] nvme-pci: improve IO performance via poll after batch submission Ming Lei
2019-11-08  3:55 ` [PATCH 1/2] nvme-pci: move sq/cq_poll lock initialization into nvme_init_queue Ming Lei
2019-11-08  4:12   ` Keith Busch
2019-11-08  7:09     ` Ming Lei
2019-11-08  3:55 ` [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue Ming Lei
2019-11-11 20:44   ` Christoph Hellwig
2019-11-12  0:33     ` Long Li
2019-11-12  1:35       ` Sagi Grimberg
2019-11-12  2:39       ` Ming Lei
2019-11-12 16:25         ` Hannes Reinecke
2019-11-12 16:49           ` Keith Busch
2019-11-12 17:29             ` Hannes Reinecke [this message]
2019-11-13  3:05               ` Ming Lei
2019-11-13  3:17                 ` Keith Busch
2019-11-13  3:57                   ` Ming Lei
2019-11-12 21:20         ` Long Li
2019-11-12 21:36           ` Keith Busch
2019-11-13  0:50             ` Long Li
2019-11-13  2:24           ` Ming Lei
2019-11-12  2:07     ` Ming Lei
2019-11-12  1:44   ` Sagi Grimberg
2019-11-12  9:56     ` Ming Lei
2019-11-12 17:35       ` Sagi Grimberg
2019-11-12 21:17         ` Long Li
2019-11-12 23:44         ` Jens Axboe
2019-11-13  2:47         ` Ming Lei
2019-11-12 18:11   ` Nadolski, Edmund
2019-11-13 13:46     ` Ming Lei

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