Re: [patch 00/52] x86: Rework the vector management

Juergen Gross
2017-09-14T11:21:58Z

On 13/09/17 23:29, Thomas Gleixner wrote:
> Sorry for the large CC list, but this is a major surgery.
>
> The vector management in x86 including the surrounding code is a
> conglomorate of ancient bits and pieces which have been subject to
> 'modernization' and featuritis over the years. The most obscure parts are
> the vector allocation mechanics, the cleanup vector handling and the cpu
> hotplug machinery. Replacing these pieces of art was on my todo list for a
> long time.
>
> Recent attempts to 'solve' CPU offline / hibernation issues which are
> partially caused by the current vector management implementation made me
> look for real. Further information in this thread:
>
> http://lkml.kernel.org/r/cover.1504235838.git.yu.c.chen@intel.com
>
> Aside of drivers allocating gazillion of interrupts, there are quite some
> things which can be addressed in the x86 vector management and in the core
> code.
>
> - Multi CPU affinities:
>
> A dubious property which is not available on all machines and causes
> major complexity both in the allocator and the cleanup/hotplug
> management. See:
>
> http://lkml.kernel.org/r/alpine.DEB.2.20.1709071045440.1827@nanos
>
> - Priority level spreading:
>
> An obscure and undocumented property which I think is sufficiently
> argued to be not required in:
>
> http://lkml.kernel.org/r/alpine.DEB.2.20.1709071045440.1827@nanos
>
> - Allocation of vectors when interrupt descriptors are allocated.
>
> This is a historical implementation detail, which is not really
> required when the vector allocation is delayed up to the point when
> request_irq() is invoked. This might make request_irq() fail, when the
> vector space is exhausted, but drivers should handle request_irq()
> fails anyway.
>
> The upside of changing this is that the active vector space becomes
> smaller especially on hibernation/cpu offline when drivers shut down
> queue interrupts of outgoing CPUs.
>
> Some of this is already addressed with the managed interrupt facility,
> but that was bolted on top of the existing vector management because
> proper integration was not possible at that point. I take the blame
> for this, but the tradeoff of not doing it would have been more
> broken driver boiler plate code all over the place. So I went for the
> lesser of two evils.
>
> - Allocation of vectors on the wrong place
>
> Even for managed interrupts the vector allocation at descriptor
> allocation happens on the wrong place and gets fixed after the fact
> with a call to set_affinity(). In case of not remapped interrupts
> this results in at least one interrupt on the wrong CPU before it is
> migrated to the desired target.
>
> - Lack of instrumentation
>
> All of this is a black box which allows no insight into the actual
> vector usage.
>
> The series addresses these points and converts the x86 vector management to
> a bitmap based allocator which provides proper reservation management for
> 'managed interrupts' and best effort reservation for regular interrupts.
> The latter allows overcommitment, which 'fixes' some of hotplug/hibernation
> problems in a clean way. It can't fix all of them depending on the driver
> involved.
>
> This rework is no excuse for driver writers to do exhaustive vector
> allocations instead of utilizing the managed interrupt infrastructure, but
> it addresses long standing issues in this code with the side effect of
> mitigating some of the driver oddities. The proper solution for multi queue
> management are 'managed interrupts' which has been proven in the block-mq
> work as they solve issues which are worked around in other drivers in
> creative ways with lots of copied code and often enough broken attempts to
> handle interrupt affinity and CPU hotplug problems.
>
> The new bitmap allocator and the x86 vector management code are
> instrumented with tracepoints and the irq domain debugfs files allow deep
> insight into the vector allocation and reservations.
>
> The patches work on machines with and without interrupt remapping and
> inside of KVM guests of various flavours, though I have no idea what I
> broke on the way with other hypervisors, posted interrupts etc. So I kindly
> ask for your support in testing and review.
>
> The series applies on top of Linus tree and is available as git branch:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.x86/apic
>
> Note, that this branch is Linus tree plus scheduler and x86 fixes which I
> required to do proper testing. They have outstanding pull requests and
> might be merged already when you read this.
>
> Thanks,
>
> tglx
> ---
> arch/x86/include/asm/x2apic.h | 49 -
> b/arch/x86/Kconfig | 1
> b/arch/x86/include/asm/apic.h | 255 +-----
> b/arch/x86/include/asm/desc.h | 2
> b/arch/x86/include/asm/hw_irq.h | 6
> b/arch/x86/include/asm/io_apic.h | 2
> b/arch/x86/include/asm/irq.h | 4
> b/arch/x86/include/asm/irq_vectors.h | 8
> b/arch/x86/include/asm/irqdomain.h | 5
> b/arch/x86/include/asm/kvm_host.h | 2
> b/arch/x86/include/asm/trace/irq_vectors.h | 244 ++++++
> b/arch/x86/kernel/apic/Makefile | 2
> b/arch/x86/kernel/apic/apic.c | 38 -
> b/arch/x86/kernel/apic/apic_common.c | 46 +
> b/arch/x86/kernel/apic/apic_flat_64.c | 10
> b/arch/x86/kernel/apic/apic_noop.c | 25
> b/arch/x86/kernel/apic/apic_numachip.c | 12
> b/arch/x86/kernel/apic/bigsmp_32.c | 8
> b/arch/x86/kernel/apic/htirq.c | 5
> b/arch/x86/kernel/apic/io_apic.c | 94 --
> b/arch/x86/kernel/apic/msi.c | 5
> b/arch/x86/kernel/apic/probe_32.c | 29
> b/arch/x86/kernel/apic/vector.c | 1090 +++++++++++++++++------------
> b/arch/x86/kernel/apic/x2apic.h | 9
> b/arch/x86/kernel/apic/x2apic_cluster.c | 196 +----
> b/arch/x86/kernel/apic/x2apic_phys.c | 44 +
> b/arch/x86/kernel/apic/x2apic_uv_x.c | 17
> b/arch/x86/kernel/i8259.c | 1
> b/arch/x86/kernel/idt.c | 12
> b/arch/x86/kernel/irq.c | 101 --
> b/arch/x86/kernel/irqinit.c | 1
> b/arch/x86/kernel/setup.c | 12
> b/arch/x86/kernel/smpboot.c | 14
> b/arch/x86/kernel/traps.c | 2
> b/arch/x86/kernel/vsmp_64.c | 19
> b/arch/x86/platform/uv/uv_irq.c | 5
> b/arch/x86/xen/apic.c | 6
> b/drivers/gpio/gpio-xgene-sb.c | 7
> b/drivers/iommu/amd_iommu.c | 44 -
> b/drivers/iommu/intel_irq_remapping.c | 43 -
> b/drivers/irqchip/irq-gic-v3-its.c | 5
> b/drivers/pinctrl/stm32/pinctrl-stm32.c | 5
> b/include/linux/irq.h | 22
> b/include/linux/irqdesc.h | 1
> b/include/linux/irqdomain.h | 14
> b/include/linux/msi.h | 5
> b/include/trace/events/irq_matrix.h | 201 +++++
> b/kernel/irq/Kconfig | 3
> b/kernel/irq/Makefile | 1
> b/kernel/irq/autoprobe.c | 2
> b/kernel/irq/chip.c | 37
> b/kernel/irq/debugfs.c | 12
> b/kernel/irq/internals.h | 19
> b/kernel/irq/irqdesc.c | 3
> b/kernel/irq/irqdomain.c | 43 -
> b/kernel/irq/manage.c | 18
> b/kernel/irq/matrix.c | 443 +++++++++++
> b/kernel/irq/msi.c | 32
> 58 files changed, 2133 insertions(+), 1208 deletions(-)

Complete series tested with paravirt + xen enabled 64 bit kernel:

bare metal boot okay
boot as Xen dom0 okay
boot as Xen pv-domU okay
boot as Xen HVM-domU with PV-drivers okay
Vcpu onlining/offlining in pv-domU okay

So you can add my:

Tested-by: Juergen Gross <jgross@suse.com>
Acked-by: Juergen Gross <jgross@suse.com>

Juergen