On Fri, 1 May 2015, Ingo Molnar wrote: > > * Vince Weaver <vincent.wea...@maine.edu> wrote: > > > So this is just a warning, and I've reported it before, but the > > perf_fuzzer triggers this fairly regularly on my Haswell system. > > > > It looks like fixed counter 0 (retired instructions) being set to > > 0000fffffffffffe occasionally causes an irq loop storm and gets > > stuck until the PMU state is cleared. > > So 0000fffffffffffe corresponds to 2 events left until overflow, > right? And on Haswell we don't set x86_pmu.limit_period AFAICS, so we > allow these super short periods. > > Maybe like on Broadwell we need a quirk on Nehalem/Haswell as well, > one similar to bdw_limit_period()? Something like the patch below?
I spent the morning trying to get a reproducer for this. It turns out to be complex. It seems in addition to fixed counter 0 being set to -2, at least one other non-fixed counter must be about to overflow. For example, in this case gen-PMC2 is also poised to overflow at the same time. CPU#0: gen-PMC2 ctrl: 00000003ff96764b CPU#0: gen-PMC2 count: 0000000000000001 gen-PMC2 left: 0000ffffffffffff ... [ 2408.612442] CPU#0: fixed-PMC0 count: 0000fffffffffffe It's not always PMC2 but in the warnings there's at least one other gen-PMC about to overflow at the exact same time as the fixed one. Vince -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
