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xen-ia64-devel
RE: [Xen-ia64-devel] SMP-g design notes
>From: Tristan Gingold
>Sent: 2006年3月8日 17:34
>[Comments are welcome]
>
>SMP-guest (SMP-g) current design.
>
>Because it is design time, here are some note about my SMP-g work.
>The current patch is very small. I tried only to bring-up SMP-g ASAP to catch
>more
>SMP bugs. Also I tried to miminize Linux kernel changes.
>
>The only Linux kernel change is the way IPI are sent. When running_on_xen,
>the write into
>LSAPIC is replaced by a physdev_op hypercall.
Talk early to xen mailing list, if there's really necessity to add a new
physdev_op since all that type of operations is defined under public
header directory.
>
>The xen changes are:
>
>* LID is virtualized. In fact this was achieved with my vIOSAPIC patch. I am
>planning
>to modify this so that SMP-g can be done without vIOSAPIC.
Glad to see that.
>The virtualized LID is ID=EID=vcpu_id.
>From the SDM, lower order bits of 'id' is a unique address of local system
bus, and then higher order bits of 'id' together with 'eid' corresponds to an
unique address of local system bus within entire system. Though not forced,
will it better to conform to SDM description to keep user's convention? For
example, only let lower order bits of 'id' equal to vcpu_id, with rest bits
with
same value for all VCPUs since we can simply present guest with one
system bus.
>
>* ACPI LSAPIC entries are enabled for dom0 and added for domU.
> For dom0, I have added a dom0_maxcpu= command line parameter to set
>the
>maximum number
> of dom0 vcpu.
Not sure whether typo. Please keep same as x86, which is "dom0_max_vcpus="
option.
>
>* SAL_VECTOR_OS_BOOT_RENDEZ added to set iip and r1 of non-running
>vcpu.
Hope you are adding that emulation in sal_emulator (dom_fw.c), instead of
the hack occurring in your last vIOSAPIC patch where it's handled within IPI
emulation. :-)
>
>* SAL wakeup descriptor added.
>
>* physdev_op added to accept and deliver IPI as an interrupt. It also handle
>vcpu start-up.
Once again, please consult xen mailing list if adding new physdev_op.
>
>* ITC_DRIFT feature added to SAL descriptors. This avoids clock
>synchronizations which
> can't be currently done since itc is not virtualized.
So I believe this is only temporary hack, which should be removed once itc
virtualization is added. Or else xenlinux won't register the interpolator which
may affect the accuracy because guest may assume there's another platform
timer resource as reference.
>
>* ptc.ga is a real problem: currently an IPI is sent in Xen to purge the VHPT.
>Performance
> may be very bad. We should think about this.
>
>
Yes, emulation of ptc.ga will be more complex than other emulations. However
simply talking about the claim above, IPI is a necessity IMO, if another vcpu
is
running on another LP at the emulation. Though we may add some lazy flush
later.
Thanks,
Kevin
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