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scx_lavd: improve the accuracy of cpu utilization calculation

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When a cpu is idle for a whole interval, its idle time does not
correctlyh adds up so the utilization of such cpu tends to be higher
than the actual utilization. Now it is fixedk, so cpu utilization
becomes more accurate.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
This commit is contained in:
Changwoo Min 2024-08-30 13:42:57 +09:00
parent 2f8cc0d60f
commit 5ecaa9ebe2
1 changed files with 7 additions and 6 deletions
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13
scheds/rust/scx_lavd/src/bpf/main.bpf.c
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@ -593,6 +593,7 @@ static void init_sys_stat_ctx(struct sys_stat_ctx *c)
c->stat_next = get_sys_stat_next();
c->now = bpf_ktime_get_ns();
c->duration = c->now - c->stat_cur->last_update_clk;
c->stat_next->last_update_clk = c->now;
}
static void collect_sys_stat(struct sys_stat_ctx *c)
@ -649,7 +650,7 @@ static void collect_sys_stat(struct sys_stat_ctx *c)
bool ret = __sync_bool_compare_and_swap(
&cpuc->idle_start_clk, old_clk, c->now);
if (ret) {
c->idle_total += c->now - old_clk;
cpuc->idle_total += c->now - old_clk;
break;
}
}
@ -660,6 +661,7 @@ static void collect_sys_stat(struct sys_stat_ctx *c)
u64 compute = 0;
if (c->duration > cpuc->idle_total)
compute = c->duration - cpuc->idle_total;
c->new_util = (compute * LAVD_CPU_UTIL_MAX) / c->duration;
cpuc->util = calc_avg(cpuc->util, c->new_util);
@ -691,9 +693,9 @@ static void calc_sys_stat(struct sys_stat_ctx *c)
c->duration_total = c->duration * nr_cpus_onln;
if (c->duration_total > c->idle_total)
c->compute_total = c->duration_total - c->idle_total;
c->new_util = (c->compute_total * LAVD_CPU_UTIL_MAX) /
c->duration_total;
else
c->compute_total = 0;
c->new_util = (c->compute_total * LAVD_CPU_UTIL_MAX)/c->duration_total;
if (c->sched_nr == 0) {
/*
@ -757,7 +759,6 @@ static void do_update_sys_stat(void)
/*
* Make the next version atomically visible.
*/
c.stat_next->last_update_clk = c.now;
flip_sys_stat();
}
@ -772,7 +773,7 @@ static u64 calc_nr_active_cpus(struct sys_stat *stat_cur)
nr_active /= (LAVD_CC_PER_CORE_MAX_CTUIL * 1000);
/*
* If a few CPUs are particularly busy, boost the overflow CPUs by 2x.
* If a few CPUs are particularly busy, boost the active CPUs more.
*/
nr_active += min(LAVD_CC_NR_OVRFLW, (stat_cur->nr_violation) / 1000);
nr_active = max(min(nr_active, nr_cpus_onln),