linux-kernel - Re: [PATCH] nvme: utilize two queue maps, one for reads and one for writes

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Date:   Wed, 14 Nov 2018 10:12:44 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     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: utilize two queue maps, one for reads and one for
 writes

On 11/13/18 9:52 PM, Guenter Roeck wrote:
> On Tue, Nov 13, 2018 at 05:51:08PM -0700, Jens Axboe wrote:
>> On 11/13/18 5:41 PM, Guenter Roeck wrote:
>>> Hi,
>>>
>>> On Wed, Oct 31, 2018 at 08:36:31AM -0600, Jens Axboe wrote:
>>>> NVMe does round-robin between queues by default, which means that
>>>> sharing a queue map for both reads and writes can be problematic
>>>> in terms of read servicing. It's much easier to flood the queue
>>>> with writes and reduce the read servicing.
>>>>
>>>> Implement two queue maps, one for reads and one for writes. The
>>>> write queue count is configurable through the 'write_queues'
>>>> parameter.
>>>>
>>>> By default, we retain the previous behavior of having a single
>>>> queue set, shared between reads and writes. Setting 'write_queues'
>>>> to a non-zero value will create two queue sets, one for reads and
>>>> one for writes, the latter using the configurable number of
>>>> queues (hardware queue counts permitting).
>>>>
>>>> Reviewed-by: Hannes Reinecke <hare@...e.com>
>>>> Reviewed-by: Keith Busch <keith.busch@...el.com>
>>>> Signed-off-by: Jens Axboe <axboe@...nel.dk>
>>>
>>> This patch causes hangs when running recent versions of
>>> -next with several architectures; see the -next column at
>>> kerneltests.org/builders for details.  Bisect log below; this
>>> was run with qemu on alpha. Reverting this patch as well as
>>> "nvme: add separate poll queue map" fixes the problem.
>>
>> I don't see anything related to what hung, the trace, and so on.
>> Can you clue me in? Where are the test results with dmesg?
>>
> alpha just stalls during boot. parisc reports a hung task
> in nvme_reset_work. sparc64 reports EIO when instantiating
> the nvme driver, called from nvme_reset_work, and then stalls.
> In all three cases, reverting the two mentioned patches fixes
> the problem.

I think the below patch should fix it.

> https://kerneltests.org/builders/qemu-parisc-next/builds/173/steps/qemubuildcommand_1/logs/stdio
> 
> is an example log for parisc.
> 
> I didn't check if the other boot failures (ppc looks bad)
> have the same root cause.
> 
>> How to reproduce?
>>
> parisc:
> 
> 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
> 
> alpha:
> 
> qemu-system-alpha -M clipper -kernel arch/alpha/boot/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' \
> 	-m 128M -nographic -monitor null -serial stdio
> 
> sparc64:
> 
> qemu-system-sparc64 -M sun4u -cpu 'TI UltraSparc IIi' -m 512 \
> 	-snapshot -device nvme,serial=foo,drive=d0,bus=pciB \
> 	-drive file=rootfs.ext2,if=none,format=raw,id=d0 \
> 	-kernel arch/sparc/boot/image -no-reboot \
> 	-append 'root=/dev/nvme0n1 rw rootwait panic=-1 console=ttyS0' \
> 	-nographic -monitor none
> 
> The root file systems are available from the respective subdirectories
> of:
> 
> https://github.com/groeck/linux-build-test/tree/master/rootfs

This is useful, thanks! I haven't tried it yet, but I was able to
reproduce on x86 with MSI turned off.


diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 8df868afa363..6c03461ad988 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2098,7 +2098,7 @@ static int nvme_setup_irqs(struct nvme_dev *dev, int nr_io_queues)
 		.nr_sets = ARRAY_SIZE(irq_sets),
 		.sets = irq_sets,
 	};
-	int result;
+	int result = 0;
 
 	/*
 	 * For irq sets, we have to ask for minvec == maxvec. This passes
@@ -2113,9 +2113,16 @@ static int nvme_setup_irqs(struct nvme_dev *dev, int nr_io_queues)
 			affd.nr_sets = 1;
 
 		/*
-		 * Need IRQs for read+write queues, and one for the admin queue
+		 * Need IRQs for read+write queues, and one for the admin queue.
+		 * If we can't get more than one vector, we have to share the
+		 * admin queue and IO queue vector. For that case, don't add
+		 * an extra vector for the admin queue, or we'll continue
+		 * asking for 2 and get -ENOSPC in return.
 		 */
-		nr_io_queues = irq_sets[0] + irq_sets[1] + 1;
+		if (result == -ENOSPC && nr_io_queues == 1)
+			nr_io_queues = 1;
+		else
+			nr_io_queues = irq_sets[0] + irq_sets[1] + 1;
 
 		result = pci_alloc_irq_vectors_affinity(pdev, nr_io_queues,
 				nr_io_queues,

-- 
Jens Axboe