This patch removes the redundant module prefix used in the pr_err() when
nvmet_get_smart_log_nsid() failed to find the namespace provided as a part
of smart-log command.
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Signed-off-by: Milan P. Gandhi <mgandhi@redhat.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Merge -rc6 in, for two reasons:

1) Resolve a trivial conflict in the blk-mq-tag.c documentation
2) A few important regression fixes went into upstream directly, so
   they aren't in the 4.20 branch.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

* tag 'v4.19-rc6': (780 commits)
  Linux 4.19-rc6
  MAINTAINERS: fix reference to moved drivers/{misc => auxdisplay}/panel.c
  cpufreq: qcom-kryo: Fix section annotations
  perf/core: Add sanity check to deal with pinned event failure
  xen/blkfront: correct purging of persistent grants
  Revert "xen/blkfront: When purging persistent grants, keep them in the buffer"
  selftests/powerpc: Fix Makefiles for headers_install change
  blk-mq: I/O and timer unplugs are inverted in blktrace
  dax: Fix deadlock in dax_lock_mapping_entry()
  x86/boot: Fix kexec booting failure in the SEV bit detection code
  bcache: add separate workqueue for journal_write to avoid deadlock
  drm/amd/display: Fix Edid emulation for linux
  drm/amd/display: Fix Vega10 lightup on S3 resume
  drm/amdgpu: Fix vce work queue was not cancelled when suspend
  Revert "drm/panel: Add device_link from panel device to DRM device"
  xen/blkfront: When purging persistent grants, keep them in the buffer
  clocksource/drivers/timer-atmel-pit: Properly handle error cases
  block: fix deadline elevator drain for zoned block devices
  ACPI / hotplug / PCI: Don't scan for non-hotplug bridges if slot is not bridge
  drm/syncobj: Don't leak fences when WAIT_FOR_SUBMIT is set
  ...
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Miguel writes:
  "A trivial fix for auxdisplay

    - MAINTAINERS reference fix for moved file
      Reported by Joe Perches"

* tag 'auxdisplay-for-greg-v4.19-rc6' of https://github.com/ojeda/linux:
  MAINTAINERS: fix reference to moved drivers/{misc => auxdisplay}/panel.c

Merge tag 'libnvdimm-fixes2-4.19-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm

Dan writes:
  "filesystem-dax for 4.19-rc6

   Fix a deadlock in the new for 4.19 dax_lock_mapping_entry() routine."

* tag 'libnvdimm-fixes2-4.19-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm:
  dax: Fix deadlock in dax_lock_mapping_entry()

Commit 51c1e9b5 ("auxdisplay: Move panel.c to drivers/auxdisplay folder")
moved the file, but the MAINTAINERS reference was not updated.

Link: https://lore.kernel.org/lkml/20180928220131.31075-1-joe@perches.com/Reported-by: Joe Perches <joe@perches.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

Jens writes:
  "Block fixes for 4.19-rc6

   A set of fixes that should go into this release. This pull request
   contains:

   - A fix (hopefully) for the persistent grants for xen-blkfront. A
     previous fix from this series wasn't complete, hence reverted, and
     this one should hopefully be it. (Boris Ostrovsky)

   - Fix for an elevator drain warning with SMR devices, which is
     triggered when you switch schedulers (Damien)

   - bcache deadlock fix (Guoju Fang)

   - Fix for the block unplug tracepoint, which has had the
     timer/explicit flag reverted since 4.11 (Ilya)

   - Fix a regression in this series where the blk-mq timeout hook is
     invoked with the RCU read lock held, hence preventing it from
     blocking (Keith)

   - NVMe pull from Christoph, with a single multipath fix (Susobhan Dey)"

* tag 'for-linus-20180929' of git://git.kernel.dk/linux-block:
  xen/blkfront: correct purging of persistent grants
  Revert "xen/blkfront: When purging persistent grants, keep them in the buffer"
  blk-mq: I/O and timer unplugs are inverted in blktrace
  bcache: add separate workqueue for journal_write to avoid deadlock
  xen/blkfront: When purging persistent grants, keep them in the buffer
  block: fix deadline elevator drain for zoned block devices
  blk-mq: Allow blocking queue tag iter callbacks
  nvme: properly propagate errors in nvme_mpath_init

Thomas writes:
  "A single fix for the AMD memory encryption boot code so it does not
   read random garbage instead of the cached encryption bit when a kexec
   kernel is allocated above the 32bit address limit."

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/boot: Fix kexec booting failure in the SEV bit detection code

Thomas writes:
  "Three small fixes for clocksource drivers:
   - Proper error handling in the Atmel PIT driver
   - Add CLOCK_SOURCE_SUSPEND_NONSTOP for TI SoCs so suspend works again
   - Fix the next event function for Facebook Backpack-CMM BMC chips so
     usleep(100) doesnt sleep several milliseconds"

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  clocksource/drivers/timer-atmel-pit: Properly handle error cases
  clocksource/drivers/fttmr010: Fix set_next_event handler
  clocksource/drivers/ti-32k: Add CLOCK_SOURCE_SUSPEND_NONSTOP flag for non-am43 SoCs

Thomas writes:
  "A single fix for a missing sanity check when a pinned event is tried
  to be read on the wrong CPU due to a legit event scheduling failure."

* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/core: Add sanity check to deal with pinned event failure

Rafael writes:
  "Power management fix for 4.19-rc6

   Fix incorrect __init and __exit annotations in the Qualcomm
   Kryo cpufreq driver (Nathan Chancellor)."

* tag 'pm-4.19-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  cpufreq: qcom-kryo: Fix section annotations

There is currently a warning when building the Kryo cpufreq driver into
the kernel image:

WARNING: vmlinux.o(.text+0x8aa424): Section mismatch in reference from
the function qcom_cpufreq_kryo_probe() to the function
.init.text:qcom_cpufreq_kryo_get_msm_id()
The function qcom_cpufreq_kryo_probe() references
the function __init qcom_cpufreq_kryo_get_msm_id().
This is often because qcom_cpufreq_kryo_probe lacks a __init
annotation or the annotation of qcom_cpufreq_kryo_get_msm_id is wrong.

Remove the '__init' annotation from qcom_cpufreq_kryo_get_msm_id
so that there is no more mismatch warning.

Additionally, Nick noticed that the remove function was marked as
'__init' when it should really be marked as '__exit'.

Fixes: 46e2856b (cpufreq: Add Kryo CPU scaling driver)
Fixes: 5ad7346b (cpufreq: kryo: Add module remove and exit)
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: 4.18+ <stable@vger.kernel.org> # 4.18+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Christoph writes:
  "dma mapping fix for 4.19-rc6

   fix a missing Kconfig symbol for commits introduced in 4.19-rc"

* tag 'dma-mapping-4.19-3' of git://git.infradead.org/users/hch/dma-mapping:
  dma-mapping: add the missing ARCH_HAS_SYNC_DMA_FOR_CPU_ALL declaration

Dmitry writes:
  "Input updates for v4.19-rc5

   Just a few driver fixes"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input:
  Input: uinput - allow for max == min during input_absinfo validation
  Input: elantech - enable middle button of touchpad on ThinkPad P72
  Input: atakbd - fix Atari CapsLock behaviour
  Input: atakbd - fix Atari keymap
  Input: egalax_ts - add system wakeup support
  Input: gpio-keys - fix a documentation index issue

Mark writes:
  "spi: Fixes for v4.19

   Quite a few fixes for the Renesas drivers in here, plus a fix for the
   Tegra driver and some documentation fixes for the recently added
   spi-mem code.  The Tegra fix is relatively large but fairly
   straightforward and mechanical, it runs on probe so it's been
   reasonably well covered in -next testing."

* tag 'spi-fix-v4.19-rc5' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi:
  spi: spi-mem: Move the DMA-able constraint doc to the kerneldoc header
  spi: spi-mem: Add missing description for data.nbytes field
  spi: rspi: Fix interrupted DMA transfers
  spi: rspi: Fix invalid SPI use during system suspend
  spi: sh-msiof: Fix handling of write value for SISTR register
  spi: sh-msiof: Fix invalid SPI use during system suspend
  spi: gpio: Fix copy-and-paste error
  spi: tegra20-slink: explicitly enable/disable clock

Merge tag 'regulator-v4.19-rc5' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator

Mark writes:
  "regulator: Fixes for 4.19

   A collection of fairly minor bug fixes here, a couple of driver
   specific ones plus two core fixes.  There's one fix for the new
   suspend state code which fixes some confusion with constant values
   that are supposed to indicate noop operation and another fixing a
   race condition with the creation of sysfs files on new regulators."

* tag 'regulator-v4.19-rc5' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator:
  regulator: fix crash caused by null driver data
  regulator: Fix 'do-nothing' value for regulators without suspend state
  regulator: da9063: fix DT probing with constraints
  regulator: bd71837: Disable voltage monitoring for LDO3/4

Michael writes:
  "powerpc fixes for 4.19 #3

   A reasonably big batch of fixes due to me being away for a few weeks.

   A fix for the TM emulation support on Power9, which could result in
   corrupting the guest r11 when running under KVM.

   Two fixes to the TM code which could lead to userspace GPR corruption
   if we take an SLB miss at exactly the wrong time.

   Our dynamic patching code had a bug that meant we could patch freed
   __init text, which could lead to corrupting userspace memory.

   csum_ipv6_magic() didn't work on little endian platforms since we
   optimised it recently.

   A fix for an endian bug when reading a device tree property telling
   us how many storage keys the machine has available.

   Fix a crash seen on some configurations of PowerVM when migrating the
   partition from one machine to another.

   A fix for a regression in the setup of our CPU to NUMA node mapping
   in KVM guests.

   A fix to our selftest Makefiles to make them work since a recent
   change to the shared Makefile logic."

* tag 'powerpc-4.19-3' of https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  selftests/powerpc: Fix Makefiles for headers_install change
  powerpc/numa: Use associativity if VPHN hcall is successful
  powerpc/tm: Avoid possible userspace r1 corruption on reclaim
  powerpc/tm: Fix userspace r13 corruption
  powerpc/pseries: Fix unitialized timer reset on migration
  powerpc/pkeys: Fix reading of ibm, processor-storage-keys property
  powerpc: fix csum_ipv6_magic() on little endian platforms
  powerpc/powernv/ioda2: Reduce upper limit for DMA window size (again)
  powerpc: Avoid code patching freed init sections
  KVM: PPC: Book3S HV: Fix guest r11 corruption with POWER9 TM workarounds

Linus writes:
  "Pin control fixes for v4.19:
   - Fixes to x86 hardware:
   - AMD interrupt debounce issues
   - Faulty Intel cannonlake register offset
   - Revert pin translation IRQ locking"

* tag 'pinctrl-v4.19-4' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl:
  Revert "pinctrl: intel: Do pin translation when lock IRQ"
  pinctrl: cannonlake: Fix HOSTSW_OWN register offset of H variant
  pinctrl/amd: poll InterruptEnable bits in amd_gpio_irq_set_type

It is possible that a failure can occur during the scheduling of a
pinned event. The initial portion of perf_event_read_local() contains
the various error checks an event should pass before it can be
considered valid. Ensure that the potential scheduling failure
of a pinned event is checked for and have a credible error.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: acme@kernel.org
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/6486385d1f30336e9973b24c8c65f5079543d3d3.1537377064.git.reinette.chatre@intel.com

We apply a smoothing to the scale changes in order to keep sawtoothy
behavior from occurring.  However our window for checking if we've
missed our target can sometimes be lower than the smoothing interval
(500ms), especially on faster drives like ssd's.  In order to deal with
this keep track of the running tally of the previous intervals that we
threw away because we had already done a scale event recently.

This is needed for the ssd case as these low latency drives will have
bursts of latency, and if it happens to be ok for the window that
directly follows the opening of the scale window we could unthrottle
when previous windows we were missing our target.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We use an average latency approach for determining if we're missing our
latency target.  This works well for rotational storage where we have
generally consistent latencies, but for ssd's and other low latency
devices you have more of a spikey behavior, which means we often won't
throttle misbehaving groups because a lot of IO completes at drastically
faster times than our latency target.  Instead keep track of how many
IO's miss our target and how many IO's are done in our time window.  If
the p(90) latency is above our target then we know we need to throttle.
With this change in place we are seeing the same throttling behavior
with our testcase on ssd's as we see with rotational drives.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

There is logic to keep cgroups that haven't done a lot of IO in the most
recent scale window from being punished for over-active higher priority
groups.  However for things like ssd's where the windows are pretty
short we'll end up with small numbers of samples, so 5% of samples will
come out to 0 if there aren't enough.  Make the floor 1 sample to keep
us from improperly bailing out of scaling down.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Hitting the case where blk_queue_depth() returned 1 uncovered the fact
that iolatency doesn't actually handle this case properly, it simply
doesn't scale down anybody.  For this case we should go straight into
applying the time delay, which we weren't doing.  Since we already limit
the floor at 1 request this if statement is not needed, and this allows
us to set our depth to 1 which allows us to apply the delay if needed.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We were using blk_queue_depth() assuming that it would return
nr_requests, but we hit a case in production on drives that had to have
NCQ turned off in order for them to not shit the bed which resulted in a
qd of 1, even though the nr_requests was much larger.  iolatency really
only cares about requests we are allowed to queue up, as any io that
get's onto the request list is going to be serviced soonish, so we want
to be throttling before the bio gets onto the request list.  To make
iolatency work as expected, simply use q->nr_requests instead of
blk_queue_depth() as that is what we actually care about.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Dave writes:
  "drm fixes for 4.19-rc6

   Looks like a pretty normal week for graphics,

   core: syncobj fix, panel link regression revert
   amd: suspend/resume fixes, EDID emulation fix
   mali-dp: NV12 writeback and vblank reset fixes
   etnaviv: DMA setup fix"

* tag 'drm-fixes-2018-09-28' of git://anongit.freedesktop.org/drm/drm:
  drm/amd/display: Fix Edid emulation for linux
  drm/amd/display: Fix Vega10 lightup on S3 resume
  drm/amdgpu: Fix vce work queue was not cancelled when suspend
  Revert "drm/panel: Add device_link from panel device to DRM device"
  drm/syncobj: Don't leak fences when WAIT_FOR_SUBMIT is set
  drm/malidp: Fix writeback in NV12
  drm: mali-dp: Call drm_crtc_vblank_reset on device init
  drm/etnaviv: add DMA configuration for etnaviv platform device

Merge tag 'riscv-for-linus-4.19-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/riscv-linux

Palmer writes:
  "A Single RISC-V Update for 4.19-rc6

   The Debian guys have been pushing on our port and found some
   unversioned symbols leaking into modules.  This PR contains a single
   fix for that issue."

* tag 'riscv-for-linus-4.19-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/riscv-linux:
  RISC-V: include linux/ftrace.h in asm-prototypes.h

NSEC_PER_SEC has type long, so 5 * NSEC_PER_SEC is calculated as a long.
However, 5 seconds is 5,000,000,000 nanoseconds, which overflows a
32-bit long. Make sure all of the targets are calculated as 64-bit
values.

Fixes: 6e25cb01 ("kyber: implement improved heuristics")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Bjorn writes:
  "PCI fixes:

  - Fix ACPI hotplug issue that causes black screen crash at boot (Mika
    Westerberg)

  - Fix DesignWare "scheduling while atomic" issues (Jisheng Zhang)

  - Add PPC contacts to MAINTAINERS for PCI core error handling (Bjorn
    Helgaas)

  - Sort Mobiveil MAINTAINERS entry (Lorenzo Pieralisi)"

* tag 'pci-v4.19-fixes-2' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/helgaas/pci:
  ACPI / hotplug / PCI: Don't scan for non-hotplug bridges if slot is not bridge
  PCI: dwc: Fix scheduling while atomic issues
  MAINTAINERS: Move mobiveil PCI driver entry where it belongs
  MAINTAINERS: Update PPC contacts for PCI core error handling

Pull NVMe fix from Christoph.

* 'nvme-4.19' of git://git.infradead.org/nvme:
  nvme: properly propagate errors in nvme_mpath_init

Commit a46b5367 ("xen/blkfront: cleanup
stale persistent grants") introduced a regression as purged persistent
grants were not pu into the list of free grants again. Correct that.
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Fix didn't work for all cases, reverting to add a (hopefully)
better fix.

This reverts commit f151ba98.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Use new-style DEVICE_ATTR_RO/DEVICE_ATTR_RW to create the sysfs attributes
and register the disk with default sysfs attribute groups.
Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Register default sysfs groups during device_add_disk() to avoid a
race condition with udev during startup.
Signed-off-by: Hannes Reinecke <hare@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Register default sysfs groups during device_add_disk() to avoid a
race condition with udev during startup.
Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Ed L. Cachin <ed.cashin@acm.org>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We should be registering the ns_id attribute as default sysfs
attribute groups, otherwise we have a race condition between
the uevent and the attributes appearing in sysfs.
Suggested-by: Bart van Assche <bvanassche@acm.org>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Update device_add_disk() to take an 'groups' argument so that
individual drivers can register a device with additional sysfs
attributes.
This avoids race condition the driver would otherwise have if these
groups were to be created with sysfs_add_groups().
Signed-off-by: Martin Wilck <martin.wilck@suse.com>
Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Commit b2d35fa5 ("selftests: add headers_install to lib.mk")
introduced a requirement that Makefiles more than one level below the
selftests directory need to define top_srcdir, but it didn't update
any of the powerpc Makefiles.

This broke building all the powerpc selftests with eg:

  make[1]: Entering directory '/src/linux/tools/testing/selftests/powerpc'
  BUILD_TARGET=/src/linux/tools/testing/selftests/powerpc/alignment; mkdir -p $BUILD_TARGET; make OUTPUT=$BUILD_TARGET -k -C alignment all
  make[2]: Entering directory '/src/linux/tools/testing/selftests/powerpc/alignment'
  ../../lib.mk:20: ../../../../scripts/subarch.include: No such file or directory
  make[2]: *** No rule to make target '../../../../scripts/subarch.include'.
  make[2]: Failed to remake makefile '../../../../scripts/subarch.include'.
  Makefile:38: recipe for target 'alignment' failed

Fix it by setting top_srcdir in the affected Makefiles.

Fixes: b2d35fa5 ("selftests: add headers_install to lib.mk")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

When debugging Kyber, it's really useful to know what latencies we've
been having, how the domain depths have been adjusted, and if we've
actually been throttling. Add three tracepoints, kyber_latency,
kyber_adjust, and kyber_throttled, to record that.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Kyber's current heuristics have a few flaws:

- It's based on the mean latency, but p99 latency tends to be more
  meaningful to anyone who cares about latency. The mean can also be
  skewed by rare outliers that the scheduler can't do anything about.
- The statistics calculations are purely time-based with a short window.
  This works for steady, high load, but is more sensitive to outliers
  with bursty workloads.
- It only considers the latency once an I/O has been submitted to the
  device, but the user cares about the time spent in the kernel, as
  well.

These are shortcomings of the generic blk-stat code which doesn't quite
fit the ideal use case for Kyber. So, this replaces the statistics with
a histogram used to calculate percentiles of total latency and I/O
latency, which we then use to adjust depths in a slightly more
intelligent manner:

- Sync and async writes are now the same domain.
- Discards are a separate domain.
- Domain queue depths are scaled by the ratio of the p99 total latency
  to the target latency (e.g., if the p99 latency is double the target
  latency, we will double the queue depth; if the p99 latency is half of
  the target latency, we can halve the queue depth).
- We use the I/O latency to determine whether we should scale queue
  depths down: we will only scale down if any domain's I/O latency
  exceeds the target latency, which is an indicator of congestion in the
  device.

These new heuristics are just as scalable as the heuristics they
replace.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>