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Date: Sat, 8 Dec 2018 22:22:31 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Jens Axboe <axboe@...nel.dk>
Cc: Christoph Hellwig <hch@....de>,
Keith Busch <keith.busch@...el.com>,
Sagi Grimberg <sagi@...mberg.me>,
linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: default to 0 poll queues
On 12/8/18 9:38 PM, Jens Axboe wrote:
> On 12/8/18 5:49 PM, Guenter Roeck wrote:
>> Hi,
>>
>> On Mon, Nov 19, 2018 at 08:18:24AM -0700, Jens Axboe wrote:
>>> We need a better way of configuring this, and given that polling is
>>> (still) a bit niche, let's default to using 0 poll queues. That way
>>> we'll have the same read/write/poll behavior as 4.20, and users that
>>> want to test/use polling are required to do manual configuration of the
>>> number of poll queues.
>>>
>>> Reviewed-by: Christoph Hellwig <hch@....de>
>>> Signed-off-by: Jens Axboe <axboe@...nel.dk>
>>> ---
>>
>> This patch results in a boot stall when booting parisc (hppa) images
>> from nvme in qemu.
>>
>> ...
>> Fusion MPT SAS Host driver 3.04.20
>> rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
>> rcu: (detected by 0, t=5252 jiffies, g=141, q=22)
>> rcu: All QSes seen, last rcu_sched kthread activity 5252 (-66742--71994), jiffies_till_next_fqs=1, root ->qsmask 0x0
>> kworker/u8:3 R running task 0 85 2 0x00000004
>> Workqueue: nvme-reset-wq nvme_reset_work
>> Backtrace:
>> [<10190d20>] show_stack+0x28/0x38
>> [<101dd1e0>] sched_show_task.part.3+0xc4/0x144
>> [<101dd290>] sched_show_task+0x30/0x38
>> [<10221e18>] rcu_check_callbacks+0x760/0x7a4
>>
>> rcu: rcu_sched kthread starved for 5252 jiffies! g141 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
>> rcu: RCU grace-period kthread stack dump:
>> rcu_sched R running task 0 10 2 0x00000000
>> Backtrace:
>> [<10995b1c>] __schedule+0x214/0x648
>> [<10995f94>] schedule+0x44/0xa8
>> [<1099a7c4>] schedule_timeout+0x114/0x1a0
>> [<10220e70>] rcu_gp_kthread+0x744/0x968
>> [<101d5438>] kthread+0x154/0x15c
>> [<1019501c>] ret_from_kernel_thread+0x1c/0x24
>>
>> [ continued ]
>>
>> This is only seen in SMP configurations; non-SMP configurations are ok.
>> Reverting the patch fixes the problem. v4.20-rcX and earlier kernels
>> also boot without problems.
>>
>> For reference, here is the qemu command line. This is with qemu 3.0.
>>
>> qemu-system-hppa -kernel vmlinux -no-reboot \
>> -snapshot \
>> -device nvme,serial=foo,drive=d0 \
>> -drive file=rootfs.ext2,if=none,format=raw,id=d0 \
>> -append 'root=/dev/nvme0n1 rw rootwait panic=-1 console=ttyS0,115200 ' \
>> -nographic -monitor null
>>
>> Please let me know if you need additional information.
>
> Hmm, I think the queue reduction case has a logic error. Actually there
> are two bugs:
>
> 1) Ensure we don't keep overwriting the queue count we ask for
> 2) Don't include poll_queues in the vectors we need
>
> Untested... And not super pretty. But does this work for you?
>
It solves the boot problem on parisc/hppa. I didn't test with any other architectures.
Should I run a complete test sequence ?
Guenter
>
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 7732c4979a4e..fe00e19493ae 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -2083,7 +2083,7 @@ static void nvme_calc_io_queues(struct nvme_dev *dev, unsigned int nr_io_queues)
> }
> }
>
> -static int nvme_setup_irqs(struct nvme_dev *dev, int nr_io_queues)
> +static int nvme_setup_irqs(struct nvme_dev *dev, int irq_queues, int pqueues)
> {
> struct pci_dev *pdev = to_pci_dev(dev->dev);
> int irq_sets[2];
> @@ -2100,7 +2100,8 @@ static int nvme_setup_irqs(struct nvme_dev *dev, int nr_io_queues)
> * IRQ vector needs.
> */
> do {
> - nvme_calc_io_queues(dev, nr_io_queues);
> + nvme_calc_io_queues(dev, irq_queues + pqueues);
> + pqueues = dev->io_queues[HCTX_TYPE_POLL];
> irq_sets[0] = dev->io_queues[HCTX_TYPE_DEFAULT];
> irq_sets[1] = dev->io_queues[HCTX_TYPE_READ];
> if (!irq_sets[1])
> @@ -2111,11 +2112,11 @@ static int nvme_setup_irqs(struct nvme_dev *dev, int nr_io_queues)
> * 1 + 1 queues, just ask for a single vector. We'll share
> * that between the single IO queue and the admin queue.
> */
> - if (!(result < 0 && nr_io_queues == 1))
> - nr_io_queues = irq_sets[0] + irq_sets[1] + 1;
> + if (!(result < 0 || irq_queues == 1))
> + irq_queues = irq_sets[0] + irq_sets[1] + 1;
>
> - result = pci_alloc_irq_vectors_affinity(pdev, nr_io_queues,
> - nr_io_queues,
> + result = pci_alloc_irq_vectors_affinity(pdev, irq_queues,
> + irq_queues,
> PCI_IRQ_ALL_TYPES | PCI_IRQ_AFFINITY, &affd);
>
> /*
> @@ -2125,12 +2126,12 @@ static int nvme_setup_irqs(struct nvme_dev *dev, int nr_io_queues)
> * likely does not. Back down to ask for just one vector.
> */
> if (result == -ENOSPC) {
> - nr_io_queues--;
> - if (!nr_io_queues)
> + irq_queues--;
> + if (!irq_queues)
> return result;
> continue;
> } else if (result == -EINVAL) {
> - nr_io_queues = 1;
> + irq_queues = 1;
> continue;
> } else if (result <= 0)
> return -EIO;
> @@ -2144,7 +2145,7 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
> {
> struct nvme_queue *adminq = &dev->queues[0];
> struct pci_dev *pdev = to_pci_dev(dev->dev);
> - int result, nr_io_queues;
> + int result, want_irqs, nr_io_queues, pqueues;
> unsigned long size;
>
> nr_io_queues = max_io_queues();
> @@ -2185,7 +2186,20 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
> */
> pci_free_irq_vectors(pdev);
>
> - result = nvme_setup_irqs(dev, nr_io_queues);
> + /*
> + * If we don't get the number of IO queues we asked for, see if we
> + * need to adjust the number of poll queues down
> + */
> + pqueues = poll_queues;
> + if (!pqueues)
> + want_irqs = nr_io_queues;
> + else if (pqueues >= nr_io_queues) {
> + want_irqs = 1;
> + pqueues = nr_io_queues - 1;
> + } else
> + want_irqs = nr_io_queues - pqueues;
> +
> + result = nvme_setup_irqs(dev, want_irqs, pqueues);
> if (result <= 0)
> return -EIO;
>
>
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