[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH, v2] reduce 'd' debug key's global impact
On 06/05/2010 10:07, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote: >>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 06.05.10 10:01 >>> >> Although I suppose the event-check vector has a cleaner interface for >> calling it and should be implemented for all architectures. If you add >> whatever new flag you need to irq_cpustat_t then it would be cheap to check, >> being a definite cache hit. I suppose each cpu would > > Actually, in smp_event_check_interrupt(), irq_cpustat isn't being used > so far, so placing the new field there wouldn't be a definite cache hit. > Instead (if that has to remain, which I doubt) co-locating it with > __irq_regs would help here. The most interesting exit path out of the handler via ret_from_intr will pass through test_all_events (because that indicates a busy CPU running a guest, and in that case we are most likely to have interrupted guest context). In that case we pull in the irqstat cacheline to check softirq_pending. Other exit paths indicate idle CPU (don't care so much about that) or interrupted hypervisor context (should be rarer than running in guest context for a non-idle CPU). > Otoh it seems like I will should add irq_enter()/irq_exit() now that the > function calls something non-trivial... Yes, most definitely. They are cheap and should be added unconditionally to the handler if you go this route. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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