Add xen-platform-pci-bar-uc key in xenstore to activate AMD xen-pci MMIO WB cache for grant table #6555
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ocaml/idl/datamodel_vm.ml
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| ~allowed_roles:_R_VM_ADMIN ~doc_tags:[Windows] () | ||
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| let set_xen_platform_pci_bar_uc = | ||
| call ~name:"set_xen_platform_pci_bar_uc" ~lifecycle: [] |
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I think this is too low level of a setting to be exposed as-is from xapi.
What's preventing the setting to be simply always disabled so the perf improvement is always present?
- The version of xen? xenopsd should be aware of the xen version in use and select the option.
- The guest kernel? Then a field in the VM object should be added (no need for new calls to set it) (maybe Hvm_mmio_bar)
- ...
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This is enabled by default in new versions of hvmloader. Xapi change is to allow disabling this optimization in case something is wrong
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I tend to agree with @psafont that this should not be exposed in the VM data model. Otherwise all kind of low-level and Xen-specific parameters end up here.
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This is enabled by default in new versions of hvmloader. Xapi change is to allow disabling this optimization in case something is wrong.
Then I'm not convinced this setting should be per-vm, nor that it should be exposed in the API.
In first instance, if there's a problem, it should be treated as a bug bug. If we want to have a workaround / failsafe while the issue is being fixed and release, a configuration option in xenopsd.conf should be enough to enable a workaround for the bug
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Thank you for the feedbacks. I will close this PR to work in this new direction. I will create a new PR with the changes on xenopsd only.
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@robhoes suggested yesterday that perhaps this might be too low-level for a separate call and it might be worth putting this option into |
This patch add a new parameter named 'xen-platform-pci-bar-uc' who has a default value of 'true' to keep the default behavior of hvmloader. Putting 'false' to this parameter will tell xenopsd to add a xenstore key of '0' in: '/local/domain/<domid>/hvmloader/pci/xen-platform-pci-bar-uc'. Only this key set to 0 will change the behavior of hvmloader. This changeset is link to this xen commit: https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=22650d6054625be10172fe0c78b9cadd1a39bd63 Signed-off-by: Anthoine Bourgeois <[email protected]>
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This patch add a new parameter named 'xen-platform-pci-bar-uc' in xenopsd config file who has a default value of 'true' to keep the default behavior of hvmloader. Putting 'false' to this parameter will tell xenopsd to add a xenstore key of '0' in: '/local/domain/<domid>/hvmloader/pci/xen-platform-pci-bar-uc'. Only this key set to 0 will change the behavior of hvmloader. Otherwise, xenstore is set with '1' by default. This changeset is link to this xen commit: https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=22650d6054625be10172fe0c78b9cadd1a39bd63 This is a new and much more simpler version of: #6555
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This patch add a new parameter named 'xen-platform-pci-bar-uc' who has a default value of 'true' to keep the default behavior of hvmloader. Putting 'false' to this parameter will tell xenopsd to add a xenstore key of '0' in:
'/local/domain//hvmloader/pci/xen-platform-pci-bar-uc'.
Only this key set to 0 will change the behavior of hvmloader.
This changeset is link to this xen commit:
x86/hvmloader: select xen platform pci MMIO BAR UC or WB MTRR cache attribute