* Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Tue, 17 Oct 2017, Ingo Molnar wrote: > > * Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > > On Tue, 17 Oct 2017, Ingo Molnar wrote: > > > > No, please fix performance. > > > > > > You know very well that with the cross release stuff we have to take the > > > performance hit of stack unwinding because we have no idea whether there > > > will show up a new lock relation later or not. And there is not much you > > > can do in that respect. > > > > > > OTOH, the cross release feature unearthed real deadlocks already so it is a > > > valuable debug feature and having an explicit config switch which defaults > > > to N is well worth it. > > > > I disagree, because even if that's correct, the choices are not binary. The > > performance regression was a slowdown of around 7x: lockdep boot overhead on that > > particula system went from +3 seconds to +21 seconds... > > Hmm, I might have missed something, but what I've seen in this thread is: > > > > > Boot time (from "Linux version" to login prompt) had in fact doubled > > > > since 4.13 where it took 17 seconds (with my current config) compared to > > > > the 35 seconds I now see with 4.14-rc4. > > So that's 2x not 7x. [...] Yeah, so what you missed I think is that the no-lockdep bootup time is 14 seconds. So we have: vanilla: 14 secs lockdep: 17 secs (+3 secs) lockdep+crossrelease: 35 secs (+21 secs) So lockdep overhead got 7x worse on this system. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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