On 8/22/15 12:23 AM, Ian Lepore wrote:
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
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).
remind me again why it cant spin with a 'halt' instruction?
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.
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