On 2015-04-20 20:33, Radim Krčmář wrote: > 2015-04-20 19:45+0200, Jan Kiszka: >> On 2015-04-20 19:37, Jan Kiszka wrote: >>> On 2015-04-20 19:33, Radim Krčmář wrote: >>>> 2015-04-20 19:21+0200, Jan Kiszka: >>>>> On 2015-04-20 19:16, Radim Krčmář wrote: >>>>>> 2015-04-20 18:14+0200, Radim Krčmář: >>>>>>> Tested-by: Radim Krčmář <rkrc...@redhat.com> >>>>>> >>>>>> Uncached accesses were roughly 20x slower. >>>>>> In case anyone wanted to reproduce, I used this as a kvm-unit-test: >>>>>> >>>>>> --- >>>> | [code] >>>>> >>>>> Great, thanks. Will you push it to the unit tests? Could raise >>>>> motivations to fix the !NPT/EPT case. >>>> >>>> It can't be included in `run_tests.sh`, because we intenionally ignore >>>> PAT for normal RAM on VMX and the test does "fail" ... >>> >>> That ignoring is encoded into the EPT? > > Yes, it's the VMX_EPT_IPAT_BIT. > >> And do you also know why is it ignored on Intel? Side effects on the host? > > I think it is an optimization exclusive to Intel. > We know that the other side is not real hardware, which could avoid CPU > caches when accessing memory, so there is little reason to slow the > guest down.
If the guest pushes data for DMA into RAM, it may assume that it lands there directly, without the need for explicit flushes, because it has caching disabled - no? Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
