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I will drop patch #1 and #2 and use this one (with a commit log >>>> and some more tests), given it's based on the work of Joel, Lyude and >>>> me, would the following tags make sense to all of you? >>>>> Co-developed-by: Joel Fernandes >>> >>> I don't know, I am not a big fan of the alternative patch because it adds a >>> per-cpu counter anyway if !CONFIG_PREEMPT_LONG [1]. And it is also a much bigger >>> patch than the one I wrote. Purely from an objective perspective, I would still >>> want to keep my original patch because it is simple. What is really the >>> objection to it? >>> > > PREEMPT_LONG is an architecture-specific way to improve the performance > IMO. Just to be clear, do you object it at all, or do you object > combining it with your original patch? If it's the latter, I could make > another patch as a follow to enable PREEMPT_LONG. When I looked at the alternative patch, I did consider that it was overcomplicated and it should be justified. Otherwise, I don't object to it. It seems to be a matter of preference I think. I would prefer a simpler fix than an overcomplicated fix for a hypothetical issue (unless we have data showing issue). If it was a few lines of change, that'd be different story. > >>> [1] >>> +#ifndef CONFIG_PREEMPT_LONG >>> +/* >>> + * Any 32bit architecture that still cares about performance should >>> + * probably ensure this is near preempt_count. >>> + */ >>> +DEFINE_PER_CPU(unsigned int, nmi_nesting); >>> +#endif >>> >> If the objection to my patch is modifying a per-cpu counter, isn't NMI a slow >> path? If we agree, then keeping things simple is better IMO unless we have data > > I guess Peter was trying to say it's not a slow path if you consider > perf event interrupts on x86? [1] How are we handling this performance issue then on 32-bit x86 architecture with perf? Or are we saying we don't care about performance on 32-bit? -- Joel Fernandes