RFC xl: add cpuid config file option
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| # | Subject and files | Size | Replies | Applied |
|---|---|---|---|---|
| 1/2 | xl: add cpuid parametertools/ tools/ tools/ +2 more | +29 | 7 replies | |
| 2/2 | xl: add cpuid parsing and translationtools/ | +209 | 0 replies |
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Cover letter [PATCH 0/2] [RFC] xl: add cpuid config file option
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:
Quoted 4 lines
#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"
Quoted 9 lines
# 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"
Quoted 9 lines
# 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.
Regards,
Andre.
Signature · 3 lines
Andre Przywara AMD-Operating System Research Center (OSRC), Dresden, Germany Tel: +49 351 448-3567-12