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[Xen-devel] Re: [PATCH 0/7] PV on HVM: receive interrupts as xen events

To: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 0/7] PV on HVM: receive interrupts as xen events
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Thu, 02 Sep 2010 12:04:24 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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 On 08/30/2010 04:20 AM, Stefano Stabellini wrote:
> Hi all,
> this patch series introduces some performance improvements for xen PV on
> HVM guests: interacting with the emulated APIC is slow because it causes
> traps in the hypervisor while receiving xen events using the vector callback
> mechanism allow us to skip all that. For this reason we remap interrupts
> and MSIs into xen pirqs so that from that point on we can receive them
> as xen events instead.
> This series is based on Konrad's pcifront series (not upstream yet):
> http://lkml.org/lkml/2010/8/4/374
> and requires a patch to xen and a patch to qemu-xen (just sent to
> xen-devel).

My only concern with this series is the pirq remapping stuff.  Why do
pirq and irq need to be non-identical?  Is it because pirq is a global
namespace, and dom0 has already assigned it?

Why do guests need to know about max pirq?  Would it be better to make
Xen use a more dynamic structure for pirqs so that any arbitrary value
can be used?


> The list of patches with diffstat follows:
> Jeremy Fitzhardinge (2):
>  xen: add xen hvm acpi_register_gsi variant
>  acpi: use indirect call to register gsi in different modes
> Stefano Stabellini (5):
>  xen: xen: map MSIs into pirqs
>  xen: support GSI -> pirq remapping in PV on HVM guests
>  xen: implement xen_hvm_register_pirq
>  xen: get the maximum number of pirqs from xen
>  xen: support pirq != irq
>  arch/x86/include/asm/acpi.h      |    3 +
>  arch/x86/include/asm/xen/pci.h   |   10 +++
>  arch/x86/kernel/acpi/boot.c      |   60 ++++++++++++++------
>  arch/x86/pci/xen.c               |  114 
> ++++++++++++++++++++++++++++++++++++++
>  drivers/pci/xen-pcifront.c       |    2 +-
>  drivers/xen/events.c             |  106 +++++++++++++++++++++++++++++++----
>  include/xen/events.h             |    3 +
>  include/xen/interface/features.h |    3 +
>  include/xen/interface/physdev.h  |   36 ++++++++++++
>  9 files changed, 308 insertions(+), 29 deletions(-)
> A git tree with this series and Konrad's pcifront series on top of Linux
> 2.6.36-rc1 is available here:
> git://xenbits.xen.org/people/sstabellini/linux-pvhvm.git 
> 2.6.36-rc1-pvhvm-pirq-v3
> Cheers,
> Stefano Stabellini

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