Re: [PATCH v6 08/16] sched/cpufreq: uclamp: Add utilization clamping for FAIR tasks
From: Peter Zijlstra <peterz@infradead.org>
Date: 2019-01-22 17:13:29
Also in:
linux-pm, lkml
On Tue, Jan 15, 2019 at 10:15:05AM +0000, Patrick Bellasi wrote:
quoted hunk ↗ jump to hunk
@@ -342,11 +350,24 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time, return; sg_cpu->iowait_boost_pending = true; + /* + * Boost FAIR tasks only up to the CPU clamped utilization. + * + * Since DL tasks have a much more advanced bandwidth control, it's + * safe to assume that IO boost does not apply to those tasks.
I'm not buying that argument. IO-boost isn't related to b/w management. IO-boot is more about compensating for hidden dependencies, and those don't get less hidden for using a different scheduling class. Now, arguably DL should not be doing IO in the first place, but that's a whole different discussion.
+ * Instead, since RT tasks are not utilization clamped, we don't want
+ * to apply clamping on IO boost while there is blocked RT
+ * utilization.
+ */
+ max_boost = sg_cpu->iowait_boost_max;
+ if (!cpu_util_rt(cpu_rq(sg_cpu->cpu)))
+ max_boost = uclamp_util(cpu_rq(sg_cpu->cpu), max_boost);
+
/* Double the boost at each request */
if (sg_cpu->iowait_boost) {
sg_cpu->iowait_boost <<= 1;
- if (sg_cpu->iowait_boost > sg_cpu->iowait_boost_max)
- sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
+ if (sg_cpu->iowait_boost > max_boost)
+ sg_cpu->iowait_boost = max_boost;
return;
}Hurmph... so I'm not sold on this bit.