Re: [PATCH 0/6] IRQFD without IRQ routing, enabled for XICS

[Paolo Bonzini <pbonzini@redhat.com>]

Il 05/08/2014 14:27, Paolo Bonzini ha scritto:
> Il 30/06/2014 12:51, Paul Mackerras ha scritto:
>> This series of patches provides a way to implement IRQFD support
>> without having to implement IRQ routing, and adds IRQFD support for
>> the XICS interrupt controller emulation.  (XICS is the interrupt
>> controller defined for the pSeries machine type, used on IBM POWER
>> servers).
>>
>> The basic approach is to make it easy for code other than irqchip.c to
>> provide a mapping from a global interrupt number (GSI) to an irq
>> routing entry (struct kvm_kernel_irq_routing_entry).  To make the
>> lifetime of this routing entry easier to manage, we change the IRQFD
>> code to keep a copy of the routing entry (for the MSI fast-path case)
>> rather than a pointer to the routing entry.  Since the copy can't be
>> updated atomically, we add a seqcount_t to make sure that when reading
>> it we get a copy that hasn't been half-way updated.
>>
>> Next we replace the hard-coded accesses outside irqchip.c to the
>> fields of the kvm_irq_routing_table struct with calls to accessor
>> functions in irqchip.c, namely kvm_irq_map_gsi() and
>> kvm_irq_map_chip_pin().  That enables us to move all references to the
>> kvm_irq_routing_table struct, and the definition of that struct, into
>> irqchip.c.
>>
>> Then we move the irq notifier implementation from irqchip.c into
>> eventfd.c and add a separate Kconfig option to enable IRQFD.  With
>> that we can enable IRQFD without irq routing, which we achieve by
>> compiling in eventfd.c but not irqchip.c, and providing an alternative
>> implementation of kvm_irq_map_gsi() and kvm_irq_map_chip_pin().
>>
>> The last patch does that for XICS.  With this series I can use
>> vhost-net with KVM guests, and I see the TCP bandwidth between guest
>> and host on a POWER8 machine go from around 700MB/s to over 2GB/s.
>>
>> I would like to see this go into 3.17.
>>
>>  arch/ia64/kvm/Kconfig                |   1 +
>>  arch/powerpc/kvm/Kconfig             |   3 +
>>  arch/powerpc/kvm/book3s_hv_rm_xics.c |   5 ++
>>  arch/powerpc/kvm/book3s_xics.c       |  55 +++++++++++---
>>  arch/powerpc/kvm/book3s_xics.h       |   2 +
>>  arch/powerpc/kvm/mpic.c              |   4 +-
>>  arch/s390/kvm/Kconfig                |   1 +
>>  arch/s390/kvm/interrupt.c            |   3 +-
>>  arch/x86/kvm/Kconfig                 |   1 +
>>  include/linux/kvm_host.h             |  43 ++++-------
>>  virt/kvm/Kconfig                     |   3 +
>>  virt/kvm/eventfd.c                   | 134 ++++++++++++++++++++++++++---------
>>  virt/kvm/irq_comm.c                  |  24 +++----
>>  virt/kvm/irqchip.c                   |  98 ++++++++++---------------
>>  virt/kvm/kvm_main.c                  |   2 +-
>>  15 files changed, 227 insertions(+), 152 deletions(-)
>>
> 
> Applied for 3.17, thanks Eric and Cornelia for testing.
> 
> Paolo
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This doesn't build without CONFIG_KVM_XICS, so I had to apply a fixup
patch to move some code from being under CONFIG_HAVE_KVM_IRQCHIP or
unconditional, to being conditional on CONFIG_HAVE_KVM_IRQFD.  I'll send
the patch shortly.

Also, please look into adding a trace_kvm_set_irq call to kvm_set_irq in
arch/powerpc/kvm/book3s_xics.c.

I would have preferred these snags to be fixed before (especially since
the breakage is simply with "make ppc64_defconfig"), but it's partly my
fault for delaying the review for so long.  And the series is good work
and a very nice cleanup of the irqfd architecture.

Assuming that the linux-next merge from tomorrow is fine, I'll send the
second pull request to Linus.

Paolo