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Date: Mon, 15 Jun 2020 16:14:01 +0800
From: Xing Zhengjun <zhengjun.xing@...ux.intel.com>
To: Tao Zhou <ouwen210@...mail.com>, linux-kernel@...r.kernel.org
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
Hillf Danton <hdanton@...a.com>,
kernel test robot <rong.a.chen@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Mel Gorman <mgorman@...e.de>
Subject: Re: [LKP] [sched/fair] 6c8116c914: stress-ng.mmapfork.ops_per_sec
-38.0% regression
On 6/15/2020 1:18 PM, Tao Zhou wrote:
> Hi,
>
> On Fri, Jun 12, 2020 at 03:59:31PM +0800, Xing Zhengjun wrote:
>> Hi,
>>
>> I test the regression, it still existed in v5.7. If you have any fix
>> for it, please send it to me, I can verify it. Thanks.
>
> When busiest group is group_fully_busy and local group <= group_fully_busy
> the metric used:
>
> local group busiest group use metric
> group_fully_busy group_fully_busy avg load
> group_has_spare group_fully_busy idle cpu/task num
>
> In find_busiest_group() about this condition:
>
> 'if (busiest->group_type != group_overloaded) {'
>
> in this case, busiest type is group_fully_busy, local type <= group_fully_busy.
> in this branch, it check idle cpu and task num and can go to out_balance. That
> is to say ignore group_fully_busy other than group_has_spare(this case is done
> in calculate_imbalance()).
>
> When local group and busiest group are all group_fully_busy, need to use avg
> load to metric(in calculate_imbalance()). So give the below change:
>
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index cbcb2f71599b..0afbea39dd5a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9219,24 +9219,26 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
> */
> goto out_balanced;
>
> - if (busiest->group_weight > 1 &&
> - local->idle_cpus <= (busiest->idle_cpus + 1))
> - /*
> - * If the busiest group is not overloaded
> - * and there is no imbalance between this and busiest
> - * group wrt idle CPUs, it is balanced. The imbalance
> - * becomes significant if the diff is greater than 1
> - * otherwise we might end up to just move the imbalance
> - * on another group. Of course this applies only if
> - * on another group. Of course this applies only if
> - * there is more than 1 CPU per group.
> - */
> - goto out_balanced;
> + if (local->group_type == group_has_spare) {
> + if (busiest->group_weight > 1 &&
> + local->idle_cpus <= (busiest->idle_cpus + 1))
> + /*
> + * If the busiest group is not overloaded
> + * and there is no imbalance between this and busiest
> + * group wrt idle CPUs, it is balanced. The imbalance
> + * becomes significant if the diff is greater than 1
> + * otherwise we might end up to just move the imbalance
> + * on another group. Of course this applies only if
> + * there is more than 1 CPU per group.
> + */
> + goto out_balanced;
>
> - if (busiest->sum_h_nr_running == 1)
> - /*
> - * busiest doesn't have any tasks waiting to run
> - */
> - goto out_balanced;
> + if (busiest->sum_h_nr_running == 1)
> + /*
> + * busiest doesn't have any tasks waiting to run
> + */
> + goto out_balanced;
> + }
> }
>
> force_balance:
>
> In fact, I don't know this change can help or not, can be right or not.
> No test, no compile. If it is wrong, just ignore.
>
> Thanks
>
I apply the patch based on v5.7, the regression still existed.
=========================================================================================
tbox_group/testcase/rootfs/kconfig/compiler/nr_threads/disk/sc_pid_max/testtime/class/cpufreq_governor/ucode:
lkp-bdw-ep6/stress-ng/debian-x86_64-20191114.cgz/x86_64-rhel-7.6/gcc-7/100%/1HDD/4194304/1s/scheduler/performance/0xb000038
commit:
e94f80f6c49020008e6fa0f3d4b806b8595d17d8
6c8116c914b65be5e4d6f66d69c8142eb0648c22
v5.7
c7e6d37f60da32f808140b1b7dabcc3cde73c4cc (Tao's patch)
e94f80f6c4902000 6c8116c914b65be5e4d6f66d69c v5.7
c7e6d37f60da32f808140b1b7da
---------------- --------------------------- ---------------------------
---------------------------
%stddev %change %stddev %change
%stddev %change %stddev
\ | \ | \
| \
819250 ± 5% -10.1% 736616 ± 8% +41.2% 1156877 ±
3% +43.6% 1176246 ± 5% stress-ng.futex.ops
818985 ± 5% -10.1% 736460 ± 8% +41.2% 1156215 ±
3% +43.6% 1176055 ± 5% stress-ng.futex.ops_per_sec
1551 ± 3% -3.4% 1498 ± 5% -4.6% 1480 ±
5% -14.3% 1329 ± 11% stress-ng.inotify.ops
1547 ± 3% -3.5% 1492 ± 5% -4.8% 1472 ±
5% -14.3% 1326 ± 11% stress-ng.inotify.ops_per_sec
11292 ± 8% -2.8% 10974 ± 8% -9.4% 10225 ±
6% -10.1% 10146 ± 6% stress-ng.kill.ops
11317 ± 8% -2.6% 11023 ± 8% -9.1% 10285 ±
5% -10.3% 10154 ± 6% stress-ng.kill.ops_per_sec
28.20 ± 4% -35.4% 18.22 -33.4% 18.77
-27.7% 20.40 ± 9% stress-ng.mmapfork.ops_per_sec
2999012 ± 21% -10.1% 2696954 ± 22% -88.5% 344447 ±
11% -87.8% 364932 stress-ng.tee.ops_per_sec
7882 ± 3% -5.4% 7458 ± 4% -2.0% 7724 ±
3% -2.2% 7709 ± 4% stress-ng.vforkmany.ops
7804 ± 3% -5.2% 7400 ± 4% -2.0% 7647 ±
3% -2.1% 7636 ± 4% stress-ng.vforkmany.ops_per_sec
46745421 ± 3% -8.1% 42938569 ± 3% -5.2% 44312072 ±
4% -2.3% 45648193 stress-ng.yield.ops
46734472 ± 3% -8.1% 42926316 ± 3% -5.2% 44290338 ±
4% -2.4% 45627571 stress-ng.yield.ops_per_sec
>> =========================================================================================
>> tbox_group/testcase/rootfs/kconfig/compiler/nr_threads/disk/sc_pid_max/testtime/class/cpufreq_governor/ucode:
>>
>> lkp-bdw-ep6/stress-ng/debian-x86_64-20191114.cgz/x86_64-rhel-7.6/gcc-7/100%/1HDD/4194304/1s/scheduler/performance/0xb000038
>>
>> commit:
>> e94f80f6c49020008e6fa0f3d4b806b8595d17d8
>> 6c8116c914b65be5e4d6f66d69c8142eb0648c22
>> v5.7-rc3
>> v5.7
>>
>> e94f80f6c4902000 6c8116c914b65be5e4d6f66d69c v5.7-rc3
>> v5.7
>> ---------------- --------------------------- ---------------------------
>> ---------------------------
>> %stddev %change %stddev %change
>> %stddev %change %stddev
>> \ | \ | \
>> | \
>> 21398 ± 7% +6.5% 22781 ± 2% -14.5% 18287 ±
>> 4% -5.5% 20231 ± 14% stress-ng.clone.ops
>> 819250 ± 5% -10.1% 736616 ± 8% +34.2% 1099410 ±
>> 5% +41.2% 1156877 ± 3% stress-ng.futex.ops
>> 818985 ± 5% -10.1% 736460 ± 8% +34.2% 1099487 ±
>> 5% +41.2% 1156215 ± 3% stress-ng.futex.ops_per_sec
>> 1551 ± 3% -3.4% 1498 ± 5% -9.5% 1404 ±
>> 2% -4.6% 1480 ± 5% stress-ng.inotify.ops
>> 1547 ± 3% -3.5% 1492 ± 5% -9.5% 1400 ±
>> 2% -4.8% 1472 ± 5% stress-ng.inotify.ops_per_sec
>> 11292 ± 8% -2.8% 10974 ± 8% +1.9% 11505 ±
>> 13% -9.4% 10225 ± 6% stress-ng.kill.ops
>> 28.20 ± 4% -35.4% 18.22 -33.5% 18.75
>> -33.4% 18.77 stress-ng.mmapfork.ops_per_sec
>> 1932318 +1.5% 1961688 ± 2% -22.8% 1492231 ±
>> 2% +4.0% 2010509 ± 3% stress-ng.softlockup.ops
>> 1931679 ± 2% +1.5% 1961143 ± 2% -22.8% 1491939 ±
>> 2% +4.0% 2009585 ± 3% stress-ng.softlockup.ops_per_sec
>> 18607406 ± 6% -12.9% 16210450 ± 21% -12.7% 16238693 ±
>> 14% -8.0% 17120880 ± 13% stress-ng.switch.ops
>> 18604406 ± 6% -12.9% 16208270 ± 21% -12.7% 16237956 ±
>> 14% -8.0% 17115273 ± 13% stress-ng.switch.ops_per_sec
>> 2999012 ± 21% -10.1% 2696954 ± 22% -9.1% 2725653 ±
>> 21% -88.5% 344447 ± 11% stress-ng.tee.ops_per_sec
>> 7882 ± 3% -5.4% 7458 ± 4% -4.0% 7566 ±
>> 4% -2.0% 7724 ± 3% stress-ng.vforkmany.ops
>> 7804 ± 3% -5.2% 7400 ± 4% -3.8% 7504 ±
>> 4% -2.0% 7647 ± 3% stress-ng.vforkmany.ops_per_sec
>> 46745421 ± 3% -8.1% 42938569 ± 3% -7.8% 43078233 ±
>> 3% -5.2% 44312072 ± 4% stress-ng.yield.ops
>> 46734472 ± 3% -8.1% 42926316 ± 3% -7.8% 43067447 ±
>> 3% -5.2% 44290338 ± 4% stress-ng.yield.ops_per_sec
>>
>>
>> On 4/27/2020 8:46 PM, Vincent Guittot wrote:
>>> On Mon, 27 Apr 2020 at 13:35, Hillf Danton <hdanton@...a.com> wrote:
>>>>
>>>>
>>>> On Mon, 27 Apr 2020 11:03:58 +0200 Vincent Guittot wrote:
>>>>> On Sun, 26 Apr 2020 at 14:42, Hillf Danton wrote:
>>>>>>
>>>>>> On 4/21/2020 8:47 AM, kernel test robot wrote:
>>>>>>>
>>>>>>> Greeting,
>>>>>>>
>>>>>>> FYI, we noticed a 56.4% improvement of stress-ng.fifo.ops_per_sec due to commit:
>>>>>>>
>>>>>>>
>>>>>>> commit: 6c8116c914b65be5e4d6f66d69c8142eb0648c22 ("sched/fair: Fix condition of avg_load calculation")
>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>>>>>>>
>>>>>>> in testcase: stress-ng
>>>>>>> on test machine: 88 threads Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz with 128G memory
>>>>>>> with following parameters:
>>>>>>>
>>>>>>> nr_threads: 100%
>>>>>>> disk: 1HDD
>>>>>>> testtime: 1s
>>>>>>> class: scheduler
>>>>>>> cpufreq_governor: performance
>>>>>>> ucode: 0xb000038
>>>>>>> sc_pid_max: 4194304
>>>>>>>
>>>>>>
>>>>>> We need to handle group_fully_busy in a different way from
>>>>>> group_overloaded as task push does not help grow load balance
>>>>>> in the former case.
>>>>>
>>>>> Have you tested this patch for the UC above ? Do you have figures ?
>>>>>
>>>> No I am looking for a box of 88 threads. Likely to get access to it in
>>>> as early as three weeks.
>>>>
>>>>>> --- a/kernel/sched/fair.c
>>>>>> +++ b/kernel/sched/fair.c
>>>>>> @@ -8744,30 +8744,20 @@ find_idlest_group(struct sched_domain *s
>>>>>>
>>>>>> switch (local_sgs.group_type) {
>>>>>> case group_overloaded:
>>>>>> - case group_fully_busy:
>>>>>> - /*
>>>>>> - * When comparing groups across NUMA domains, it's possible for
>>>>>> - * the local domain to be very lightly loaded relative to the
>>>>>> - * remote domains but "imbalance" skews the comparison making
>>>>>> - * remote CPUs look much more favourable. When considering
>>>>>> - * cross-domain, add imbalance to the load on the remote node
>>>>>> - * and consider staying local.
>>>>>> - */
>>>>>> -
>>>>>> - if ((sd->flags & SD_NUMA) &&
>>>>>> - ((idlest_sgs.avg_load + imbalance) >= local_sgs.avg_load))
>>>>>> + if (100 * local_sgs.avg_load <= sd->imbalance_pct * (idlest_sgs.avg_load + imbalance))
>>>>>> + return idlest;
>>>>>
>>>>> So you have completely removed the NUMA special case without explaining why.
>>>>>
>>>> That was for the local domain that is lightly loaded, as the comment says,
>>>> it now is overloaded.
>>>
>>> The load value is not linked to the overloaded state of the group as
>>> you can be overloaded but still have a low load especially with cgroup
>>>
>>> That's also why there are 2 type of comparison:
>>> an absolute comparison for low load value
>>> and a proportional comparison for normal/high value
>>>
>>>>
>>>>> And you have also removed the tests for small load.
>>>>>
>>>> It is a heuristic I want to avoid. It can be replaced with the load of the
>>>> task in question as best effort.
>>>>
>>>>> Could you explain the rationale behind all these changes ?
>>>>>
>>>>> Also keep in mind that the current version provide +58% improvement
>>>>> for stress-ng.fifo
>>>>>
>>>> Yes it's great. I'm on the minor one.
>>>>
>>>>>> + if (local_sgs.avg_load > idlest_sgs.avg_load + imbalance)
>>>>>> + return idlest;
>>>>>> + else
>>>>>> return NULL;
>>>>>>
>>>>>> + case group_fully_busy:
>>>>>> /*
>>>>>> - * If the local group is less loaded than the selected
>>>>>> - * idlest group don't try and push any tasks.
>>>>>> + * Pushing task to the idlest group will make the target group
>>>>>> + * overloaded, leaving the local group that is overloaded fully busy,
>>>>>> + * thus we earn nothing except for the exchange of group types.
>>>>>
>>>>> For this case both local and idlest are fully busy and in this case
>>>>> one will become overloaded so you must compare the load to be fair in
>>>>> the spread of load
>>>>>
>>>> It may be sooner than thought that the newly overloaded group is looking to
>>>> push task out, and we'll see a task ping-pong if it happens.
>>>>
>>>>
>>>> --- a/kernel/sched/fair.c
>>>> +++ b/kernel/sched/fair.c
>>>> @@ -8683,15 +8683,11 @@ find_idlest_group(struct sched_domain *s
>>>> struct sched_group *idlest = NULL, *local = NULL, *group = sd->groups;
>>>> struct sg_lb_stats local_sgs, tmp_sgs;
>>>> struct sg_lb_stats *sgs;
>>>> - unsigned long imbalance;
>>>> struct sg_lb_stats idlest_sgs = {
>>>> .avg_load = UINT_MAX,
>>>> .group_type = group_overloaded,
>>>> };
>>>>
>>>> - imbalance = scale_load_down(NICE_0_LOAD) *
>>>> - (sd->imbalance_pct-100) / 100;
>>>> -
>>>> do {
>>>> int local_group;
>>>>
>>>> @@ -8743,31 +8739,26 @@ find_idlest_group(struct sched_domain *s
>>>> return idlest;
>>>>
>>>> switch (local_sgs.group_type) {
>>>> - case group_overloaded:
>>>> case group_fully_busy:
>>>> - /*
>>>> - * When comparing groups across NUMA domains, it's possible for
>>>> - * the local domain to be very lightly loaded relative to the
>>>> - * remote domains but "imbalance" skews the comparison making
>>>> - * remote CPUs look much more favourable. When considering
>>>> - * cross-domain, add imbalance to the load on the remote node
>>>> - * and consider staying local.
>>>> - */
>>>> -
>>>> - if ((sd->flags & SD_NUMA) &&
>>>> - ((idlest_sgs.avg_load + imbalance) >= local_sgs.avg_load))
>>>> - return NULL;
>>>> -
>>>> - /*
>>>> - * If the local group is less loaded than the selected
>>>> - * idlest group don't try and push any tasks.
>>>> - */
>>>> - if (idlest_sgs.avg_load >= (local_sgs.avg_load + imbalance))
>>>> - return NULL;
>>>> -
>>>> - if (100 * local_sgs.avg_load <= sd->imbalance_pct * idlest_sgs.avg_load)
>>>> - return NULL;
>>>> - break;
>>>> + return NULL;
>>>> + case group_overloaded:
>>>> + /* No push if balanced */
>>>> + if (100 * local_sgs.avg_load > sd->imbalance_pct *
>>>> + idlest_sgs.avg_load) {
>>>> + unsigned long avg_load;
>>>> +
>>>> + avg_load = task_h_load(p) + idlest_sgs.group_load;
>>>> + avg_load = (avg_load * SCHED_CAPACITY_SCALE) /
>>>> + idlest_sgs.group_capacity;
>>>> +
>>>> + if (100 * local_sgs.avg_load <= sd->imbalance_pct *
>>>> + avg_load)
>>>> + return idlest;
>>>> +
>>>> + if (local_sgs.avg_load > avg_load)
>>>> + return idlest;
>>>> + }
>>>> + return NULL;
>>>>
>>>> case group_imbalanced:
>>>> case group_asym_packing:
>>>>
>>
>> --
>> Zhengjun Xing
--
Zhengjun Xing
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