On Wed, 30 Mar 2011, Benjamin Herrenschmidt wrote: > On Tue, 2011-03-29 at 10:25 -0400, Eric B Munson wrote: > > Here I made the assumption that the hardware would never remove more events > > in > > a speculative roll back than it had added. This is not a situation I > > encoutered in my limited testing, so I didn't think underflow was possible. > > I > > will send out a V2 using the signed 32 bit delta and remeber to CC stable > > this time. > > I'm not thinking about underflow but rollover... or that isn't possible > with those counters ? IE. They don't wrap back to 0 after hitting > ffffffff ? >
They do roll over to 0 after ffffffff, but I thought that case was already covered by the perf_event_interrupt. Are you concerned that we will reset a counter and speculative roll back will underflow that counter?
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