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scx_lavd: more comments about CPU frequency scaling

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Signed-off-by: Changwoo Min <changwoo@igalia.com>
This commit is contained in:
Changwoo Min 2024-05-04 10:41:13 +09:00
parent 6892898469
commit a24e1d7adf
1 changed files with 17 additions and 4 deletions
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21
scheds/rust/scx_lavd/src/bpf/main.bpf.c
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@ -1074,7 +1074,7 @@ static int boost_lat(struct task_struct *p, struct task_ctx *taskc,
struct cpu_ctx *cpuc, bool is_wakeup)
{
u64 run_time_ft = 0, wait_freq_ft = 0, wake_freq_ft = 0;
u64 lat_cri_raw, perf_cri_raw;
u64 lat_cri_raw;
u16 static_prio;
int boost;
@ -1823,9 +1823,22 @@ static u32 calc_cpuperf_target(struct sys_cpu_util *cutil_cur,
u32 cpuperf_target;
/*
* If a task with an average performance criticality of the current CPU
* consumes 100% of CPU time, we set the CPU performance to the
* maximum.
* We determine the clock frequency of a CPU using two factors: 1) the
* current CPU utilization (cpuc->util) and 2) the current task's
* performance criticality (taskc->perf_cri) compared to the
* system-wide average performance criticality
* (cutil_cur->avg_perf_cri).
*
* When a current CPU utilization is 100%, and the current task's
* performance criticality is the same as the system-wide average
* criticality, we set the target CPU frequency to the maximum.
*
* In other words, even if CPU utilization is not so high, the target
* CPU frequency could be high when the task's performance criticality
* is high enough (i.e., boosting CPU frequency). On the other hand,
* the target CPU frequency could be low even if CPU utilization is
* high when a non-performance-critical task is running (i.e.,
* deboosting CPU frequency).
*/
max_load = cutil_cur->avg_perf_cri * 1000 /* max cpu util */;
cpu_load = taskc->perf_cri * cpuc->util;