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From: Christoph Hellwig <hch@lst.de>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: sagi@grimberg.me, linux-nvme@lists.infradead.org,
	ming.lei@redhat.com, helgaas@kernel.org,
	Keith Busch <kbusch@kernel.org>,
	tglx@linutronix.de, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 0/4] nvme: Threaded interrupt handling improvements
Date: Tue, 3 Dec 2019 08:42:02 +0100
Message-ID: <20191203074202.GD23881@lst.de> (raw)
In-Reply-To: <20191202195730.bzzldihtv37odsie@linutronix.de>

On Mon, Dec 02, 2019 at 08:57:30PM +0100, Sebastian Andrzej Siewior wrote:
> > The problem is that by doing the agressive polling we can keep one
> > CPU busy just running the irq handler and starve processes on that
> > CPU if an NVMe queue servers multiple CPUs.
> 
> and this is bad? The scheduler will move everything to other CPUs unless
> it is for pinned to this CPU. You can offload even RCU these days :)
> Performance wise it might be better to dedicate one CPU doing this work
> instead spreading it over four CPUs each doing a fraction of it and
> using same cache lines which bounce from one CPU to the next.

Ok, maybe things are getting better these days.  I remember we did need
the QUEUE_FLAG_SAME_FORCE flag back in the day to ensure I/O submitters
are properly throttled by the completions they receive.

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Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-27 17:58 Keith Busch
2019-11-27 17:58 ` [PATCH 1/4] PCI/MSI: Export __pci_msix_desc_mask_irq Keith Busch
2019-11-28  2:42   ` Sagi Grimberg
2019-11-28  3:41     ` Keith Busch
2019-11-28  7:17   ` Christoph Hellwig
2019-11-27 17:58 ` [PATCH 2/4] nvme/pci: Mask legacy and MSI in threaded handler Keith Busch
2019-11-28  3:39   ` Ming Lei
2019-11-28  3:48     ` Keith Busch
2019-11-28  3:58       ` Ming Lei
2019-11-28  4:14         ` Keith Busch
2019-11-28  8:41           ` Ming Lei
2019-11-27 17:58 ` [PATCH 3/4] nvme/pci: Mask MSIx interrupts for threaded handling Keith Busch
2019-11-28  7:19   ` Christoph Hellwig
2019-11-27 17:58 ` [PATCH 4/4] nvme/pci: Spin threaded interrupt completions Keith Busch
2019-11-28  2:46   ` Sagi Grimberg
2019-11-28  3:28     ` Keith Busch
2019-11-28  3:51       ` Ming Lei
2019-11-28  3:58         ` Keith Busch
2019-11-28  7:22   ` Christoph Hellwig
2019-11-29  9:13   ` Sebastian Andrzej Siewior
2019-11-30 18:10     ` Keith Busch
2019-12-02  1:10       ` Ming Lei
2019-12-02  1:30         ` Keith Busch
2019-12-02 16:51       ` Sebastian Andrzej Siewior
2019-11-28  7:50 ` [PATCH 0/4] nvme: Threaded interrupt handling improvements Christoph Hellwig
2019-11-28 17:59   ` Keith Busch
2019-11-29  8:30     ` Christoph Hellwig
2019-11-29  9:46 ` Sebastian Andrzej Siewior
2019-11-29 16:27   ` Keith Busch
2019-11-29 17:05     ` Sebastian Andrzej Siewior
2019-11-30 17:02       ` Keith Busch
2019-12-02 17:05         ` Sebastian Andrzej Siewior
2019-12-02 17:12           ` Christoph Hellwig
2019-12-02 18:06             ` Keith Busch
2019-12-03  7:40               ` Christoph Hellwig
2019-12-02 19:57             ` Sebastian Andrzej Siewior
2019-12-03  7:42               ` Christoph Hellwig [this message]

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