Messages in this thread | | | Date | Mon, 23 Feb 2015 10:12:42 +0200 | From | Purcareata Bogdan <> | Subject | Re: [PATCH 0/2] powerpc/kvm: Enable running guests on RT Linux |
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On 20.02.2015 17:17, Sebastian Andrzej Siewior wrote: > On 02/20/2015 04:10 PM, Paolo Bonzini wrote: >> 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
Actually, it's not just netperf. The bug triggers in the following scenarios: - running CPU intensive task (while true; do date; done) in SMP guest (even with 2 VCPUs) - running netperf in guest - running cyclictest in SMP guest
> May I please see a backtrace with context tracking which states where > the interrupts / preemption gets disabled and where the lock was taken?
Will do, I will get back to you as soon as I have it available. I will try and capture it using function trace.
> I'm not totally against this patch I just want to make sure this is not > a blind raw conversation to shup up the warning the kernel throws. > >> 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. > good :) > >> >> Paolo >> > Sebastian >
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