From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@kernel.org>
Cc: sagi@grimberg.me, bigeasy@linutronix.de,
linux-nvme@lists.infradead.org, ming.lei@redhat.com,
tglx@linutronix.de, hch@lst.de
Subject: Re: [PATCHv3 2/4] nvme/pci: Complete commands from primary handler
Date: Thu, 12 Dec 2019 10:14:09 +0100 [thread overview]
Message-ID: <20191212091408.GC2399@lst.de> (raw)
In-Reply-To: <20191209175622.1964-3-kbusch@kernel.org>
On Tue, Dec 10, 2019 at 02:56:20AM +0900, Keith Busch wrote:
> The context switch to wake the threaded interrupt handler has enough
> overhead to harm latency for low queue depth workloads. Complete one cycle
> through the completion queue in the primary handler to ensure threaded
> interrupts have no disadvantage compared to not using threaded interrupts. Wake
> the thread only if more completions remain after processing the queue
> once since that indicates a higher queue depth workload that may trigger
> frequent interrupts which would be better completed in the handler thread
> with device interrupts disabled.
>
> Completing requests from two different contexts is safe since nvme driver
> disables entry to the primary handler when it returns IRQ_WAKE_THREAD.
>
> Signed-off-by: Keith Busch <kbusch@kernel.org>
> ---
> drivers/nvme/host/pci.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index a0138e3ca0b9..e415fadf7331 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -1055,6 +1055,10 @@ static irqreturn_t nvme_irq_check(int irq, void *data)
> if (!nvme_cqe_pending(nvmeq))
> return IRQ_NONE;
>
> + nvme_irq(irq, data);
I think we can just open code nvme_irq here. That also means we can
use the return value of nvme_process_cq instead of the extra
nvme_cqe_pending check above. This also needs a good comment explaining
the scheme at least.
> + if (!nvme_cqe_pending(nvmeq))
> + return IRQ_HANDLED;
Including one explaining this check.
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next prev parent reply other threads:[~2019-12-12 9:14 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-09 17:56 [PATCHv3 0/4] nvme pci interrupt handling improvements Keith Busch
2019-12-09 17:56 ` [PATCHv3 1/4] nvme/pci: Disable interrupts for threaded handler Keith Busch
2019-12-10 15:12 ` Daniel Wagner
2019-12-10 15:28 ` Sebastian Andrzej Siewior
2019-12-10 15:54 ` Keith Busch
2019-12-10 16:44 ` Daniel Wagner
2019-12-10 16:57 ` Keith Busch
2019-12-10 17:11 ` Daniel Wagner
2019-12-12 9:09 ` Christoph Hellwig
2019-12-12 15:53 ` Keith Busch
2019-12-09 17:56 ` [PATCHv3 2/4] nvme/pci: Complete commands from primary handler Keith Busch
2019-12-10 20:00 ` Sagi Grimberg
2019-12-10 20:25 ` Keith Busch
2019-12-10 21:14 ` Sagi Grimberg
2019-12-11 17:35 ` Keith Busch
2019-12-12 0:40 ` Sagi Grimberg
2019-12-12 1:02 ` Keith Busch
2019-12-12 22:55 ` Ming Lei
2019-12-12 23:30 ` Keith Busch
2019-12-13 0:52 ` Ming Lei
2019-12-12 9:14 ` Christoph Hellwig [this message]
2019-12-09 17:56 ` [PATCHv3 3/4] nvme/pci: Remove use_threaded_interrupts Keith Busch
2019-12-12 9:14 ` Christoph Hellwig
2019-12-12 15:45 ` Keith Busch
2019-12-18 7:29 ` Ming Lei
2019-12-18 15:50 ` Keith Busch
2019-12-19 1:10 ` Ming Lei
2019-12-09 17:56 ` [PATCHv3 4/4] nvme/pci: Poll threaded completions Keith Busch
2019-12-10 17:43 ` Daniel Wagner
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