Commit 84676c1f21 ("genirq/affinity: assign vectors to all possible CPUs")
tried to spread the interrupts accross all possible CPUs to make sure that
in case of phsyical hotplug (e.g. virtualization) the CPUs which get
plugged in after the device was initialized are targeted by a hardware
queue and the corresponding interrupt.
This has a downside in cases where the ACPI tables claim that there are
more possible CPUs than present CPUs and the number of interrupts to spread
out is smaller than the number of possible CPUs. These bogus ACPI tables
are unfortunately not uncommon.
In such a case the vector spreading algorithm assigns interrupts to CPUs
which can never be utilized and as a consequence these interrupts are
unused instead of being mapped to present CPUs. As a result the performance
of the device is suboptimal.
To fix this spread the interrupt vectors in two stages:
1) Spread as many interrupts as possible among the present CPUs
2) Spread the remaining vectors among non present CPUs
On a 8 core system, where CPU 0-3 are present and CPU 4-7 are not present,
for a device with 4 queues the resulting interrupt affinity is:
1) Before 84676c1f21 ("genirq/affinity: assign vectors to all possible CPUs")
irq 39, cpu list 0
irq 40, cpu list 1
irq 41, cpu list 2
irq 42, cpu list 3
2) With 84676c1f21 ("genirq/affinity: assign vectors to all possible CPUs")
irq 39, cpu list 0-2
irq 40, cpu list 3-4,6
irq 41, cpu list 5
irq 42, cpu list 7
3) With the refined vector spread applied:
irq 39, cpu list 0,4
irq 40, cpu list 1,6
irq 41, cpu list 2,5
irq 42, cpu list 3,7
On a 8 core system, where all CPUs are present the resulting interrupt
affinity for the 4 queues is:
irq 39, cpu list 0,1
irq 40, cpu list 2,3
irq 41, cpu list 4,5
irq 42, cpu list 6,7
This is independent of the number of CPUs which are online at the point of
initialization because in such a system the offline CPUs can be easily
onlined afterwards, while in non-present CPUs need to be plugged physically
or virtually which requires external interaction.
The downside of this approach is that in case of physical hotplug the
interrupt vector spreading might be suboptimal when CPUs 4-7 are physically
plugged. Suboptimal from a NUMA point of view and due to the single target
nature of interrupt affinities the later plugged CPUs might not be targeted
by interrupts at all.
Though, physical hotplug systems are not the common case while the broken
ACPI table disease is wide spread. So it's preferred to have as many
interrupts as possible utilized at the point where the device is
initialized.
Block multi-queue devices like NVME create a hardware queue per possible
CPU, so the goal of commit 84676c1f21 to assign one interrupt vector per
possible CPU is still achieved even with physical/virtual hotplug.
[ tglx: Changed from online to present CPUs for the first spreading stage,
renamed variables for readability sake, added comments and massaged
changelog ]
Reported-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>
Link: https://lkml.kernel.org/r/20180308105358.1506-5-ming.lei@redhat.com
To support two stage irq vector spreading, it's required to add a starting point to the spreading function. No functional change, just preparatory work for the actual two stage change. [ tglx: Renamed variables, tidied up the code and massaged changelog ] Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Cc: Jens Axboe <axboe@kernel.dk> Cc: linux-block@vger.kernel.org Cc: Laurence Oberman <loberman@redhat.com> Cc: Christoph Hellwig <hch@infradead.org> Link: https://lkml.kernel.org/r/20180308105358.1506-4-ming.lei@redhat.com
No functional change, just prepare for converting to 2-stage irq vector spreading. Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Cc: Jens Axboe <axboe@kernel.dk> Cc: linux-block@vger.kernel.org Cc: Laurence Oberman <loberman@redhat.com> Cc: Christoph Hellwig <hch@infradead.org> Link: https://lkml.kernel.org/r/20180308105358.1506-3-ming.lei@redhat.com
The following patches will introduce two stage irq spreading for improving irq spread on all possible CPUs. No functional change. Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Cc: Jens Axboe <axboe@kernel.dk> Cc: linux-block@vger.kernel.org Cc: Laurence Oberman <loberman@redhat.com> Cc: Christoph Hellwig <hch@infradead.org> Link: https://lkml.kernel.org/r/20180308105358.1506-2-ming.lei@redhat.com
When the allocation of node_to_possible_cpumask fails, then
irq_create_affinity_masks() returns with a pointer to the empty affinity
masks array, which will cause malfunction.
Reorder the allocations so the masks array allocation comes last and every
failure path returns NULL.
Fixes: 9a0ef98e186d ("genirq/affinity: Assign vectors to all present CPUs")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
These config switches enable the same code in the core and the not yet converted architecture code. They can be selected both by randconfig builds and cause linker error because the same symbols are defined twice. Make the new GENERIC_IRQ_MULTI_HANDLER depend on !MULTI_IRQ_HANDLER to prevent that. The dependency will be removed once all architectures are converted over. Signed-off-by: Palmer Dabbelt <palmer@sifive.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Link: https://lkml.kernel.org/r/20180404043130.31277-4-palmer@sifive.com
Now that SPDX identifiers are in place, remove the boilerplate or references. The change in timings.c has been acked by the author. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Kate Stewart <kstewart@linuxfoundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Philippe Ombredanne <pombredanne@nexb.com> Link: https://lkml.kernel.org/r/20180314212030.668321222@linutronix.de
Add SPDX identifiers to files - which contain an explicit license boiler plate or reference - which do not contain a license reference and were not updated in the initial SPDX conversion because the license was deduced by the scanners via EXPORT_SYMBOL_GPL as GPL2.0 only. [ tglx: Moved adding identifiers from the patch which removes the references/boilerplate ] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Kate Stewart <kstewart@linuxfoundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Philippe Ombredanne <pombredanne@nexb.com> Link: https://lkml.kernel.org/r/20180314212030.668321222@linutronix.de
Use the proper SPDX-Identifier format. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Marc Zyngier <marc.zyngier@arm.com> Cc: Kate Stewart <kstewart@linuxfoundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Philippe Ombredanne <pombredanne@nexb.com> Link: https://lkml.kernel.org/r/20180314212030.492674761@linutronix.de
Remove pointless references to the file name itself and condense the information so it wastes less space. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Marc Zyngier <marc.zyngier@arm.com> Cc: Kate Stewart <kstewart@linuxfoundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Philippe Ombredanne <pombredanne@nexb.com> Link: https://lkml.kernel.org/r/20180314212030.412095827@linutronix.de