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Fix PowerMac G5 thermal management, plus likely other bugs, introduced in

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r328113 and affecting SMP systems.

The way the time is set on PowerMacs is racy and relies on all the
CPUs in the system setting a register simultaneously in a rendezvous. A
few-cycle delay can result in out-of-sync times, which can break the
scheduler and result in calls like mtx_sleep() and pause() never timing out
if the thread is migrated while sleeping. r328113 added a call to a no-op
function between the beginning of the rendezvous and setting the time that
was only called on APs and added enough cycles to cause a problematic offset.
For some reason, the fan-management code was the first place this appeared.

Clue from:	andreast
Reported by:	many
This commit is contained in:
nwhitehorn 2018-02-09 20:09:32 +00:00
parent 4b7442aede
commit 556f12ba7a
1 changed files with 12 additions and 3 deletions
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15
sys/powerpc/powerpc/mp_machdep.c
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@ -81,11 +81,20 @@ machdep_ap_bootstrap(void)
__asm __volatile("or 27,27,27");
__asm __volatile("or 6,6,6");
/* Give platform code a chance to do anything necessary */
/*
* Set timebase as soon as possible to meet an implicit rendezvous
* from cpu_mp_unleash(), which sets ap_letgo and then immediately
* sets timebase.
*
* Note that this is instrinsically racy and is only relevant on
* platforms that do not support better mechanisms.
*/
platform_smp_timebase_sync(ap_timebase, 1);
/* Give platform code a chance to do anything else necessary */
platform_smp_ap_init();
/* Initialize DEC and TB, sync with the BSP values */
platform_smp_timebase_sync(ap_timebase, 1);
/* Initialize decrementer */
decr_ap_init();
/* Serialize console output and AP count increment */