Messages in this thread | | | Date | Fri, 20 Feb 2015 16:10:47 +0100 | From | Paolo Bonzini <> | Subject | Re: [PATCH 0/2] powerpc/kvm: Enable running guests on RT Linux |
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On 20/02/2015 16:06, Sebastian Andrzej Siewior wrote: > On 02/20/2015 03:57 PM, Paolo Bonzini wrote:
>> Yes, but large latencies just mean the code has to be rewritten (x86 >> doesn't anymore do event injection in an atomic regions for example). >> Until it is, using raw_spin_lock is correct. > > It does not sound like it. It sounds more like disabling interrupts to > get things run faster and then limit it on a different corner to not > blow up everything.
"This patchset enables running KVM SMP guests with external interrupts on an underlying RT-enabled Linux. Previous to this patch, a guest with in-kernel MPIC emulation could easily panic the kernel due to preemption when delivering IPIs and external interrupts, because of the openpic spinlock becoming a sleeping mutex on PREEMPT_RT_FULL Linux".
> Max latencies was decreased "Max latency (us) 70 62" and that > is why this is done? For 8 us and possible DoS in case there are too > many cpus?
My understanding is that:
1) netperf can get you a BUG KVM, and raw_spinlock fixes that
2) cyclictest did not trigger the BUG, and you can also get reduced latency from using raw_spinlock.
I think we agree that (2) is not a factor in accepting the patch.
Paolo
>> Paolo >> > > Sebastian > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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