From: "Chris Mason" <clm@fb.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Rik van Riel <riel@surriel.com>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] fix scheduler regression from "sched/fair: Rework load_balance()"
Date: Mon, 26 Oct 2020 11:05:35 -0400 [thread overview]
Message-ID: <83A9BEDF-20BB-4BAD-AABD-0EECB92BF8DF@fb.com> (raw)
In-Reply-To: <20201026142455.GA13495@vingu-book>
On 26 Oct 2020, at 10:24, Vincent Guittot wrote:
> Le lundi 26 oct. 2020 à 08:45:27 (-0400), Chris Mason a écrit :
>> On 26 Oct 2020, at 4:39, Vincent Guittot wrote:
>>
>>> Hi Chris
>>>
>>> On Sat, 24 Oct 2020 at 01:49, Chris Mason <clm@fb.com> wrote:
>>>>
>>>> Hi everyone,
>>>>
>>>> We’re validating a new kernel in the fleet, and compared with
>>>> v5.2,
>>>
>>> Which version are you using ?
>>> several improvements have been added since v5.5 and the rework of
>>> load_balance
>>
>> We’re validating v5.6, but all of the numbers referenced in this
>> patch are
>> against v5.9. I usually try to back port my way to victory on this
>> kind of
>> thing, but mainline seems to behave exactly the same as 0b0695f2b34a
>> wrt
>> this benchmark.
>
> ok. Thanks for the confirmation
>
> I have been able to reproduce the problem on my setup.
Thanks for taking a look! Can I ask what parameters you used on
schbench, and what kind of results you saw? Mostly I’m trying to make
sure it’s a useful tool, but also the patch didn’t change things
here.
>
> Could you try the fix below ?
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9049,7 +9049,8 @@ static inline void calculate_imbalance(struct
> lb_env *env, struct sd_lb_stats *s
> * emptying busiest.
> */
> if (local->group_type == group_has_spare) {
> - if (busiest->group_type > group_fully_busy) {
> + if ((busiest->group_type > group_fully_busy) &&
> + (busiest->group_weight > 1)) {
> /*
> * If busiest is overloaded, try to fill spare
> * capacity. This might end up creating spare
> capacity
>
>
> When we calculate an imbalance at te smallest level, ie between CPUs
> (group_weight == 1),
> we should try to spread tasks on cpus instead of trying to fill spare
> capacity.
With this patch on top of v5.9, my latencies are unchanged. I’m
building against current Linus now just in case I’m missing other
fixes.
-chris
next prev parent reply other threads:[~2020-10-26 15:05 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-23 23:49 [PATCH] fix scheduler regression from "sched/fair: Rework load_balance()" Chris Mason
2020-10-26 8:39 ` Vincent Guittot
2020-10-26 12:45 ` Chris Mason
2020-10-26 14:24 ` Vincent Guittot
2020-10-26 14:38 ` Rik van Riel
2020-10-26 14:56 ` Vincent Guittot
2020-10-26 15:04 ` Rik van Riel
2020-10-26 15:42 ` Vincent Guittot
2020-10-26 15:54 ` Vincent Guittot
2020-10-26 16:04 ` Rik van Riel
2020-10-26 16:20 ` Vincent Guittot
2020-10-26 16:48 ` Chris Mason
2020-10-26 16:52 ` Vincent Guittot
2020-10-30 2:10 ` Rik van Riel
2020-10-30 9:16 ` Vincent Guittot
2020-10-26 15:05 ` Chris Mason [this message]
2020-10-26 15:18 ` Vincent Guittot
2020-10-26 15:28 ` Chris Mason
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