[Xen-devel] Re: [PATCH 0/2] [RFC] xl: add cpuid config file option

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 27 Aug 2010, Andre Przywara wrote:
> Hi,
> 
> xl is currently ignoring the cpuid= variable in the config file. As I
> don't like the current interface xm exposes (basically because it is
> complicated, unintuitive and very error prone), I implemented a new
> scheme for specifying CPUID flags policy, combining QEMU's and Xen's
> approach:
> cpuid = "<base>,<feature_name>=[01xks]*,...
> The patch includes a (preliminary) list of feature names along with
> their bit positions. The value for each feature bit copies the current
> meaning is Xen:
> 0: clear, 1: set, x: don't care/use default, k: keep from host, s: use
> host but preserve across migration
> The value can also be a number (either in hex or decimal), so things
> like "stepping=3" can be easily specified.
> To show you the advantage, I quote the example config file:
> > #cpuid=[ '1:ecx=xxxxxxxxxxx00xxxxxxxxxxxxxxxxxxx,
> > #           eax=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx' ]
> > # - Unset the SSE4 features (CPUID.1[ECX][20-19])
> > # - Default behaviour for all other bits in ECX And EAX registers.
> new version: cpuid = "host,sse4.1=0,sse4.2=0"
> > #   Expose to the guest multi-core cpu instead of multiple processors
> > # Example for intel, expose a 8-core processor :
> > #cpuid=['1:edx=xxx1xxxxxxxxxxxxxxxxxxxxxxxxxxxx,
> > #          ebx=xxxxxxxx00010000xxxxxxxxxxxxxxxx',
> > #     '4,0:eax=001111xxxxxxxxxxxxxxxxxxxxxxxxxx']
> > #  - CPUID.1[EDX][HT] : Enable HT
> > #  - CPUID.1[EBX] : Number of vcpus * 2
> > #  - CPUID.4,0[EAX] : Number of vcpus * 2 - 1
> > #vcpus=8
> new version: cpuid = "host,htt=1,proccount=16,maxcores=15"
> > # Example for amd, expose a 5-core processor :
> > # cpuid = ['1:ebx=xxxxxxxx00001010xxxxxxxxxxxxxxxx,
> > #             edx=xxx1xxxxxxxxxxxxxxxxxxxxxxxxxxxx',
> > # '0x80000001:ecx=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1x',
> > # '0x80000008:ecx=xxxxxxxxxxxxxxxxxxxxxxxxxx001001']
> > #   - CPUID.1[EBX] : Threads per Core * Cores per Socket (2 * #vcpus)
> > #   - CPUID.1[EDX][HT] : Enable HT
> > #   - CPUID.0x80000001[CmpLegacy] : Use legacy method
> > #   - CPUID.0x80000008[ECX] : #vcpus * 2 - 1
> new version: cpuid="host,htt=1,cmplegacy=1,proccount=10,nc=9"
> 
> The parse_cpuid function in xl_cmdimpl.c parses the string and
> translates it into the interface used by libxc.
> 
> If backward compatibility to the xm version is needed, I could also add
> a quirk for the old interface. Since it uses a Python list, this can be
> intercepted early in xl's parsing process and could use a compat code path.
> 
> This first version works for me, I'd like to hear your comments.
> 

I like your approach. Ian, what do you think?
We would still need another parser for backward compatibility though.
Also I think that parse_cpuid belongs to libxl instead of xl.


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