Dong, Eddie wrote: >> Yes. FlexPriority will be both faster and safer for those who have it >> than my hack. >> >> It may turn out that patching can improve performance even with >> FlexPriority: we can patch the APIC EOI write to look if any >> interrupts are pending, and only exit if the EOI will result in a new >> interrupt being injected. But it is very possible that this will not >> be necessary if we can achieve good interrupt mitigation with virtio. >> >> > Mmm, I won't say so. The issues is: A guest EOI (level triggered IRQ) > need to clear remote IRR bit in IOAPIC side and resample that pin in > IOAPIC side. > This one is not easy to do in patched code. > >
Hmm... The patched code needs to answer the question "what will happen if I EOI this vector now"? I think kvm can prepare the answer for that question, since it knows the irq is still asserted and that the mode is level-triggered. Basically the kvm lapic code has to calculate the IRR for a "speculative EOI" and post that in the shared memory block. If something changes (the IRQ line is de-asserted, for example) again it has to recalculate it. So yes, it will not be easy. -- Any sufficiently difficult bug is indistinguishable from a feature. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
