Messages in this thread | | | Date | Fri, 20 Feb 2015 15:57:28 +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 15:54, Sebastian Andrzej Siewior wrote: > Usually you see "scheduling while atomic" on -RT and convert them to > raw locks if it is appropriate. > > Bogdan wrote in 2/2 that he needs to limit the number of CPUs in oder > not cause a DoS and large latencies in the host. I haven't seen an > answer to my why question. Because if the conversation leads to > large latencies in the host then it does not look right. > > Each host PIC has a rawlock and does mostly just mask/unmask and the > raw lock makes sure the value written is not mixed up due to > preemption. > This hardly increase latencies because the "locked" path is very short. > If this conversation leads to higher latencies then the locked path is > too long and hardly suitable to become a rawlock.
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.
Paolo
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