Messages in this thread | | | Date | Fri, 13 Jul 2018 12:53:16 +0200 | From | Peter Zijlstra <> | Subject | Re: [bug] kpti, perf_event, bts: sporadic truncated trace |
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On Thu, Jul 12, 2018 at 06:22:13PM -0700, Hugh Dickins wrote: > A little "optimization" crept into alloc_bts_buffer() along the way, > which now places bts_interrupt_threshold not on a record boundary. > And Stephane has shown me the sentence in Vol 3B, 17.4.9, which says > "This address must point to an offset from the BTS buffer base that > is a multiple of the BTS record size." > > Please give the patch below a try, and let us know if it helps (if it > does not, then I think we'll need perfier expertise than I can give).
Ooh, good find!
> --- 4.18-rc4/arch/x86/events/intel/ds.c 2018-06-03 14:15:21.000000000 -0700 > +++ linux/arch/x86/events/intel/ds.c 2018-07-12 17:38:28.471378616 -0700 > @@ -408,9 +408,11 @@ static int alloc_bts_buffer(int cpu) > ds->bts_buffer_base = (unsigned long) cea; > ds_update_cea(cea, buffer, BTS_BUFFER_SIZE, PAGE_KERNEL); > ds->bts_index = ds->bts_buffer_base; > - max = BTS_RECORD_SIZE * (BTS_BUFFER_SIZE / BTS_RECORD_SIZE); > - ds->bts_absolute_maximum = ds->bts_buffer_base + max; > - ds->bts_interrupt_threshold = ds->bts_absolute_maximum - (max / 16); > + max = BTS_BUFFER_SIZE / BTS_RECORD_SIZE; > + ds->bts_absolute_maximum = ds->bts_buffer_base + > + max * BTS_RECORD_SIZE; > + ds->bts_interrupt_threshold = ds->bts_absolute_maximum - > + (max / 16) * BTS_RECORD_SIZE; > return 0; > } >
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