:hey,
:
:our lwkt_switch()/cpu_idle() code is kind of interwoven. additionally, there
are several variables on which we need to spin if there are runnable threads:
mplock and tokens.
:
:This makes it kind of hard to implement a idle loop which suspends the CPU,
using MONITOR/MWAIT.
:
:A quick explanation for those not aware how MONITOR/MWAIT works: you can
"arm" the monitoring hardware in modern intel CPUs using MONITOR. Any write to
this address (the size is implementation specific, probably 64 bytes) will
trigger the monitoring hardware. A following MWAIT will place the CPU into a
power saving state until the monitoring hardware gets triggered. There can be
other causes for a trigger, for instance interrupts.
:
:So what I'd like to have is a single variable on which I can MWAIT, even if
there are runnable threads. This could be either the mplock, or maybe a
per-CPU variable, being set if any token the CPU is waiting on gets released.
:
:Is something like this architecturally possible? I'd really love to use my
laptop, but right now it is still running too hot.
:
:cheers
: simon
I dont know the semantics of MONITOR/MWAIT. What happens if you issue
a MONITOR and the cpu takes an interrupt and issues another MONITOR/MWAIT
before returning to your MWAIT? That will govern whether/how we use the
feature because it will determine whether we need to disable interrupts
while doing the monitor/mwait sequence or not.
-Matt
Matthew Dillon
<[EMAIL PROTECTED]>
