Re: [GIT PULL] Scheduler changes for v6.8
From: Wyes Karny
Date: Sun Jan 14 2024 - 07:38:17 EST
On Sun, Jan 14, 2024 at 12:18:06PM +0100, Vincent Guittot wrote:
> Hi Wyes,
>
> Le dimanche 14 janv. 2024 à 14:42:40 (+0530), Wyes Karny a écrit :
> > On Wed, Jan 10, 2024 at 02:57:14PM -0800, Linus Torvalds wrote:
> > > On Wed, 10 Jan 2024 at 14:41, Linus Torvalds
> > > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > >
> > > > It's one of these two:
> > > >
> > > > f12560779f9d sched/cpufreq: Rework iowait boost
> > > > 9c0b4bb7f630 sched/cpufreq: Rework schedutil governor performance estimation
> > > >
> > > > one more boot to go, then I'll try to revert whichever causes my
> > > > machine to perform horribly much worse.
> > >
> > > I guess it should come as no surprise that the result is
> > >
> > > 9c0b4bb7f6303c9c4e2e34984c46f5a86478f84d is the first bad commit
> > >
> > > but to revert cleanly I will have to revert all of
> > >
> > > b3edde44e5d4 ("cpufreq/schedutil: Use a fixed reference frequency")
> > > f12560779f9d ("sched/cpufreq: Rework iowait boost")
> > > 9c0b4bb7f630 ("sched/cpufreq: Rework schedutil governor
> > > performance estimation")
> > >
> > > This is on a 32-core (64-thread) AMD Ryzen Threadripper 3970X, fwiw.
> > >
> > > I'll keep that revert in my private test-tree for now (so that I have
> > > a working machine again), but I'll move it to my main branch soon
> > > unless somebody has a quick fix for this problem.
> >
> > Hi Linus,
> >
> > I'm able to reproduce this issue with my AMD Ryzen 5600G system. But
> > only if I disable CPPC in BIOS and boot with acpi-cpufreq + schedutil.
> > (I believe for your case also CPPC is diabled as log "_CPC object is not
> > present" came). Enabling CPPC in BIOS issue not seen in my system. For
> > AMD acpi-cpufreq also uses _CPC object to determine the boost ratio.
> > When CPPC is disabled in BIOS something is going wrong and max
> > capacity is becoming zero.
> >
> > Hi Vincent, Qais,
> >
> > I have collected some data with bpftracing:
>
> Thanks for your tests results
>
> >
> > sudo bpftrace -e 'kretprobe:effective_cpu_util /cpu == 1/ { @eff_util = lhist(retval, 0, 1200, 50);} kprobe:get_next_freq /cpu == 1/ { @sugov_eff_util = lhist(arg1, 0, 1200, 50); @sugov_max_cap = lhist(arg2, 0, 1000, 2);} kretprobe:get_next_freq /cpu == 1/ { @sugov_freq = lhist(retval, 1000000, 5000000, 100000);}'
> >
> > with running: taskset -c 1 make
> >
> > issue case:
> >
> > Attaching 3 probes...
> > @eff_util:
> > [0, 50) 1263 |@ |
> > [50, 100) 517 | |
> > [100, 150) 233 | |
> > [150, 200) 297 | |
> > [200, 250) 162 | |
> > [250, 300) 98 | |
> > [300, 350) 75 | |
> > [350, 400) 205 | |
> > [400, 450) 210 | |
> > [450, 500) 16 | |
> > [500, 550) 1532 |@ |
> > [550, 600) 1026 | |
> > [600, 650) 761 | |
> > [650, 700) 876 | |
> > [700, 750) 1085 | |
> > [750, 800) 891 | |
> > [800, 850) 816 | |
> > [850, 900) 983 | |
> > [900, 950) 661 | |
> > [950, 1000) 759 | |
> > [1000, 1050) 57433 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> >
>
> ok so the output of effective_cpu_util() seems correct or at least to maw utilization
> value. In order to be correct, it means that arch_scale_cpu_capacity(cpu) is not zero
> because of :
>
> unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
> unsigned long *min,
> unsigned long *max)
> {
> unsigned long util, irq, scale;
> struct rq *rq = cpu_rq(cpu);
>
> scale = arch_scale_cpu_capacity(cpu);
>
> /*
> * Early check to see if IRQ/steal time saturates the CPU, can be
> * because of inaccuracies in how we track these -- see
> * update_irq_load_avg().
> */
> irq = cpu_util_irq(rq);
> if (unlikely(irq >= scale)) {
> if (min)
> *min = scale;
> if (max)
> *max = scale;
> return scale;
> }
> ...
> }
>
> If arch_scale_cpu_capacity(cpu) returns 0 then effective_cpu_util() should returns
> 0 too.
>
> Now see below
>
> > @sugov_eff_util:
> > [0, 50) 1074 | |
> > [50, 100) 571 | |
> > [100, 150) 259 | |
> > [150, 200) 169 | |
> > [200, 250) 237 | |
> > [250, 300) 156 | |
> > [300, 350) 91 | |
> > [350, 400) 46 | |
> > [400, 450) 52 | |
> > [450, 500) 195 | |
> > [500, 550) 175 | |
> > [550, 600) 46 | |
> > [600, 650) 493 | |
> > [650, 700) 1424 |@ |
> > [700, 750) 646 | |
> > [750, 800) 628 | |
> > [800, 850) 612 | |
> > [850, 900) 840 | |
> > [900, 950) 893 | |
> > [950, 1000) 640 | |
> > [1000, 1050) 60679 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> >
> > @sugov_freq:
> > [1400000, 1500000) 69911 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> >
> > @sugov_max_cap:
> > [0, 2) 69926 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
>
> In get_next_freq(struct sugov_policy *sg_policy, unsigned long util, unsigned long max)
>
> max is 0 and we comes from this path:
>
> static void sugov_update_single_freq(struct update_util_data *hook, u64 time,
> unsigned int flags)
> {
>
> ...
> max_cap = arch_scale_cpu_capacity(sg_cpu->cpu);
>
> if (!sugov_update_single_common(sg_cpu, time, max_cap, flags))
> return;
>
> next_f = get_next_freq(sg_policy, sg_cpu->util, max_cap);
> ...
>
> so here arch_scale_cpu_capacity(sg_cpu->cpu) returns 0 ...
>
> AFAICT, AMD platform uses the default
> static __always_inline
> unsigned long arch_scale_cpu_capacity(int cpu)
> {
> return SCHED_CAPACITY_SCALE;
> }
>
> I'm missing something here
>
> >
> >
> > good case:
> >
> > Attaching 3 probes...
> > @eff_util:
> > [0, 50) 246 |@ |
> > [50, 100) 150 |@ |
> > [100, 150) 191 |@ |
> > [150, 200) 239 |@ |
> > [200, 250) 117 | |
> > [250, 300) 2101 |@@@@@@@@@@@@@@@ |
> > [300, 350) 2284 |@@@@@@@@@@@@@@@@ |
> > [350, 400) 713 |@@@@@ |
> > [400, 450) 151 |@ |
> > [450, 500) 154 |@ |
> > [500, 550) 1121 |@@@@@@@@ |
> > [550, 600) 1901 |@@@@@@@@@@@@@ |
> > [600, 650) 1208 |@@@@@@@@ |
> > [650, 700) 606 |@@@@ |
> > [700, 750) 557 |@@@ |
> > [750, 800) 872 |@@@@@@ |
> > [800, 850) 1092 |@@@@@@@ |
> > [850, 900) 1416 |@@@@@@@@@@ |
> > [900, 950) 1107 |@@@@@@@ |
> > [950, 1000) 1051 |@@@@@@@ |
> > [1000, 1050) 7260 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> >
> > @sugov_eff_util:
> > [0, 50) 241 | |
> > [50, 100) 149 | |
> > [100, 150) 72 | |
> > [150, 200) 95 | |
> > [200, 250) 43 | |
> > [250, 300) 49 | |
> > [300, 350) 19 | |
> > [350, 400) 56 | |
> > [400, 450) 22 | |
> > [450, 500) 29 | |
> > [500, 550) 1840 |@@@@@@ |
> > [550, 600) 1476 |@@@@@ |
> > [600, 650) 1027 |@@@ |
> > [650, 700) 473 |@ |
> > [700, 750) 366 |@ |
> > [750, 800) 627 |@@ |
> > [800, 850) 930 |@@@ |
> > [850, 900) 1285 |@@@@ |
> > [900, 950) 971 |@@@ |
> > [950, 1000) 946 |@@@ |
> > [1000, 1050) 13839 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> >
> > @sugov_freq:
> > [1400000, 1500000) 648 |@ |
> > [1500000, 1600000) 0 | |
> > [1600000, 1700000) 0 | |
> > [1700000, 1800000) 25 | |
> > [1800000, 1900000) 0 | |
> > [1900000, 2000000) 0 | |
> > [2000000, 2100000) 0 | |
> > [2100000, 2200000) 0 | |
> > [2200000, 2300000) 0 | |
> > [2300000, 2400000) 0 | |
> > [2400000, 2500000) 0 | |
> > [2500000, 2600000) 0 | |
> > [2600000, 2700000) 0 | |
> > [2700000, 2800000) 0 | |
> > [2800000, 2900000) 0 | |
> > [2900000, 3000000) 0 | |
> > [3000000, 3100000) 0 | |
> > [3100000, 3125K) 0 | |
> > [3125K, 3300000) 0 | |
> > [3300000, 3400000) 0 | |
> > [3400000, 3500000) 0 | |
> > [3500000, 3600000) 0 | |
> > [3600000, 3700000) 0 | |
> > [3700000, 3800000) 0 | |
> > [3800000, 3900000) 0 | |
> > [3900000, 4000000) 23879 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> >
> > @sugov_max_cap:
> > [0, 2) 24555 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> >
> > In both case max_cap is zero but selected freq is incorrect in bad case.
>
> Also we have in get_next_freq():
> freq = map_util_freq(util, freq, max);
> --> util * freq /max
>
> If max was 0, we should have been an error ?
>
> There is something strange that I don't understand
>
> Could you trace on the return of sugov_get_util()
> the value of sg_cpu->util ?
Yeah, correct something was wrong in the bpftrace readings, max_cap is
not zero in traces.
git-5511 [001] d.h1. 427.159763: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
git-5511 [001] d.h1. 427.163733: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
git-5511 [001] d.h1. 427.163735: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
git-5511 [001] d.h1. 427.167706: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
git-5511 [001] d.h1. 427.167708: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
git-5511 [001] d.h1. 427.171678: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
git-5511 [001] d.h1. 427.171679: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
git-5511 [001] d.h1. 427.175653: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
git-5511 [001] d.h1. 427.175655: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
git-5511 [001] d.s1. 427.175665: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
git-5511 [001] d.s1. 427.175665: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
Debug patch applied:
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 95c3c097083e..5c9b3e1de7a0 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -166,6 +166,7 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
freq = get_capacity_ref_freq(policy);
freq = map_util_freq(util, freq, max);
+ trace_printk("[DEBUG] : freq %llu, util %llu, max %llu\n", freq, util, max);
if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
return sg_policy->next_freq;
@@ -199,6 +200,7 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu, unsigned long boost)
util = max(util, boost);
sg_cpu->bw_min = min;
sg_cpu->util = sugov_effective_cpu_perf(sg_cpu->cpu, util, min, max);
+ trace_printk("[DEBUG] : util %llu, sg_cpu->util %llu\n", util, sg_cpu->util);
}
/**
So, I guess map_util_freq going wrong somewhere.
Thanks,
Wyes
>
> Thanks for you help
> Vincent
>
> >
> > Thanks,
> > Wyes
> >