Date: Fri, 21 Aug 2015 10:23:13 -0600 From: Ian Lepore <ian@freebsd.org> To: Julian Elischer <julian@freebsd.org> Cc: Adrian Chadd <adrian@freebsd.org>, freebsd-current <freebsd-current@freebsd.org> Subject: Re: freebsd-head: suddenly NMI panics lead to ddb being unable to stop CPUs? Message-ID: <1440174193.242.279.camel@freebsd.org> In-Reply-To: <55D74402.70104@freebsd.org> References: <CAJ-VmomvqULP--v47qKJisQkf8VQNvxEhXK=HXEtv9MuLz4D1g@mail.gmail.com> <CAFMmRNw6tWMQ-pfXzSpEM7kRgKafB9KnK-oUhWw2_E-P91drLw@mail.gmail.com> <55D74193.4020008@FreeBSD.org> <CAJ-Vmon6xXBSMPWgNhg-RZKLuuMDP1hvXG%2BDdZ3fZdvFnan06g@mail.gmail.com> <55D74402.70104@freebsd.org>
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On Fri, 2015-08-21 at 23:30 +0800, Julian Elischer wrote: > On 8/21/15 11:25 PM, Adrian Chadd wrote: > > Ah, cool. I'll give it a whirl. > > > > I'm a little worried about having all of the other cores spinning in > > this case (mostly thermal; the machines get VERY LOUD when the CPUs > > are spinning..) > > > make each spin with the pause instruction.. and for N seconds (N being > the CPU ID) or something cpu_spinwait() is defined as ia32_pause() on i386 and amd64. The problem is that ONLY x86 arches benefit from cpu_spinwait(), it's just a nop on other arches, which turn into little radiant heaters for long spins (like while waiting for APs to be released). On ARM we have a really nice wait-for-event/signal-event pair of instructions, where WFE would be a natural for cpu_spinwait(), but would require a matching cpu_spinwake() type call to be sprinkled around to do the matching SEV instruction. -- Ian
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