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SubjectRe: [PATCH] nvme: utilize two queue maps, one for reads and one for writes
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 <>
> >> Reviewed-by: Keith Busch <>
> >> Signed-off-by: Jens Axboe <>
> >
> > This patch causes hangs when running recent versions of
> > -next with several architectures; see the -next column at
> > 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.

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?

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


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


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


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