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Boost thread priority while changing CPU frequency

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Boost the priority of user-space threads when they set
their affinity to a core to adjust its frequency.   This avoids a situation
where a CPU bound kernel thread with the same affinity is running on a
down-clocked core, and will "block" powerd from up-clocking the core
until the kernel thread yields.   This can lead to poor perfomance,
and to things potentially getting stuck on Giant.

Reviewed by:	kib (imp reviewed earlier version)
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D15246
This commit is contained in:
gallatin 2018-05-07 15:24:03 +00:00
parent 326c556da0
commit dbba18fdcc
1 changed files with 7 additions and 0 deletions
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7
sys/kern/kern_cpu.c
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@ -245,6 +245,7 @@ cf_set_method(device_t dev, const struct cf_level *level, int priority)
struct cf_saved_freq *saved_freq, *curr_freq;
struct pcpu *pc;
int error, i;
u_char pri;
sc = device_get_softc(dev);
error = 0;
@ -333,6 +334,8 @@ cf_set_method(device_t dev, const struct cf_level *level, int priority)
/* Bind to the target CPU before switching. */
pc = cpu_get_pcpu(set->dev);
thread_lock(curthread);
pri = curthread->td_priority;
sched_prio(curthread, PRI_MIN);
sched_bind(curthread, pc->pc_cpuid);
thread_unlock(curthread);
CF_DEBUG("setting abs freq %d on %s (cpu %d)\n", set->freq,
@ -340,6 +343,7 @@ cf_set_method(device_t dev, const struct cf_level *level, int priority)
error = CPUFREQ_DRV_SET(set->dev, set);
thread_lock(curthread);
sched_unbind(curthread);
sched_prio(curthread, pri);
thread_unlock(curthread);
if (error) {
goto out;
@ -357,6 +361,8 @@ cf_set_method(device_t dev, const struct cf_level *level, int priority)
/* Bind to the target CPU before switching. */
pc = cpu_get_pcpu(set->dev);
thread_lock(curthread);
pri = curthread->td_priority;
sched_prio(curthread, PRI_MIN);
sched_bind(curthread, pc->pc_cpuid);
thread_unlock(curthread);
CF_DEBUG("setting rel freq %d on %s (cpu %d)\n", set->freq,
@ -364,6 +370,7 @@ cf_set_method(device_t dev, const struct cf_level *level, int priority)
error = CPUFREQ_DRV_SET(set->dev, set);
thread_lock(curthread);
sched_unbind(curthread);
sched_prio(curthread, pri);
thread_unlock(curthread);
if (error) {
/* XXX Back out any successful setting? */