[Xen-devel] heavy P2M lock contention on guest HPET counter reads

["Jan Beulich" <JBeulich@xxxxxxxx>]

Hi,

with 40+ vCPU Win2012R2 guests we're observing apparent guest live
locks. The 'd' debug key reveals more than half of the vCPU-s doing an
inlined HPET main counter read from KeQueryPerformanceCounter(),
resulting in all of them racing for the lock at the beginning of
__get_gfn_type_access(). Assuming it is really necessary to always
take the write lock (rather than just the read one) here, would it perhaps
be reasonable to introduce a bypass in hvm_hap_nested_page_fault()
for the HPET page similar to the LAPIC one?

Thanks, Jan


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