From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Beata Michalska <beata.michalska@arm.com>,
Valentin Schneider <valentin.schneider@arm.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, corbet@lwn.net,
rdunlap@infradead.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry detection
Date: Wed, 26 May 2021 11:52:25 +0200 [thread overview]
Message-ID: <98ad8837-b9b8-ff50-5a91-8d5951ee757c@arm.com> (raw)
In-Reply-To: <20210525102945.GA24210@e120325.cambridge.arm.com>
On 25/05/2021 12:29, Beata Michalska wrote:
> On Tue, May 25, 2021 at 10:53:07AM +0100, Valentin Schneider wrote:
>> On 24/05/21 23:55, Beata Michalska wrote:
>>> On Mon, May 24, 2021 at 07:01:04PM +0100, Valentin Schneider wrote:
>>>> On 24/05/21 11:16, Beata Michalska wrote:
[...]
>>>>> +static inline int
>>>>> +asym_cpu_capacity_classify(struct sched_domain *sd,
>>>>> + const struct cpumask *cpu_map)
>>>>> +{
>>>>> + int sd_asym_flags = SD_ASYM_CPUCAPACITY | SD_ASYM_CPUCAPACITY_FULL;
>>>>> + struct asym_cap_data *entry;
>>>>> + int asym_cap_count = 0;
>>>>> +
>>>>> + if (list_is_singular(&asym_cap_list))
>>>>> + goto leave;
>>>>> +
>>>>> + list_for_each_entry(entry, &asym_cap_list, link) {
>>>>> + if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask)) {
>>>>> + ++asym_cap_count;
>>>>> + } else {
>>>>> + /*
>>>>> + * CPUs with given capacity might be offline
>>>>> + * so make sure this is not the case
>>>>> + */
>>>>> + if (cpumask_intersects(entry->cpu_mask, cpu_map)) {
>>>>> + sd_asym_flags &= ~SD_ASYM_CPUCAPACITY_FULL;
>>>>> + if (asym_cap_count > 1)
>>>>> + break;
>>>>> + }
>>>>
>>>> Readability nit: That could be made into an else if ().
>>> It could but then this way the -comment- gets more exposed.
>>> But that might be my personal perception so I can change that.
>>
>> As always those are quite subjective! Methink something like this would
>> still draw attention to the offline case:
>>
>> /*
>> * Count how many unique capacities this domain covers. If a
>> * capacity isn't covered, we need to check if any CPU with
>> * that capacity is actually online, otherwise it can be
>> * ignored.
>> */
>> if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask)) {
>> ++asym_cap_count;
>> } else if (cpumask_intersects(entry->cpu_mask, cpu_map)) {
>> sd_asym_flags &= ~SD_ASYM_CPUCAPACITY_FULL;
>> if (asym_cap_count > 1)
>> break;
>> }
> Noted.
> Will wait for some more comments before sending out 'polished' version.
For me asym_cpu_capacity_classify() is pretty hard to digest ;-) But I
wasn't able to break it. It also performs correctly on (non-existing SMT)
layer (with sd span eq. single CPU).
Something like this (separating asym_cap_list iteration and flags
construction would be easier for me. But like already said here,
it's subjective.
I left the two optimizations (list_is_singular(), break on asym_cap_count
> 1) out for now. asym_cap_list shouldn't have > 4 entries (;-)).
static inline int
asym_cpu_capacity_classify(struct sched_domain *sd,
const struct cpumask *cpu_map)
{
int sd_span_match = 0, cpu_map_match = 0, flags = 0;
struct asym_cap_data *entry;
list_for_each_entry(entry, &asym_cap_list, link) {
if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask))
++sd_span_match;
else if (cpumask_intersects(cpu_map, entry->cpu_mask))
++cpu_map_match;
}
WARN_ON_ONCE(!sd_span_match);
if (sd_span_match > 1) {
flags |= SD_ASYM_CPUCAPACITY;
if (!cpu_map_match)
flags |= SD_ASYM_CPUCAPACITY_FULL;
}
return flags;
}
BTW, how would this mechanism behave on a system with SMT and asymmetric CPU
capacity? Something EAS wouldn't allow but I guess asym_cap_list will be
constructed and the SD_ASYM_CPUCAPACITY_XXX flags will be set?
next prev parent reply other threads:[~2021-05-26 9:52 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-24 10:16 [PATCH v5 0/3] Rework CPU capacity asymmetry detection Beata Michalska
2021-05-24 10:16 ` [PATCH v5 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag Beata Michalska
2021-05-24 10:16 ` [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry detection Beata Michalska
2021-05-24 18:01 ` Valentin Schneider
2021-05-24 22:55 ` Beata Michalska
2021-05-24 23:19 ` Beata Michalska
2021-05-25 9:53 ` Valentin Schneider
2021-05-25 10:29 ` Beata Michalska
2021-05-26 9:52 ` Dietmar Eggemann [this message]
2021-05-26 12:15 ` Beata Michalska
2021-05-26 12:51 ` Beata Michalska
2021-05-26 18:17 ` Dietmar Eggemann
2021-05-26 21:40 ` Beata Michalska
2021-05-27 15:08 ` Dietmar Eggemann
2021-05-27 17:07 ` Beata Michalska
2021-06-02 17:17 ` Dietmar Eggemann
2021-06-02 19:48 ` Beata Michalska
2021-06-03 9:09 ` Dietmar Eggemann
2021-06-03 9:24 ` Beata Michalska
2021-05-26 18:17 ` Dietmar Eggemann
2021-05-26 21:43 ` Beata Michalska
2021-05-27 7:03 ` Peter Zijlstra
2021-05-27 12:22 ` Dietmar Eggemann
2021-05-27 12:32 ` Beata Michalska
2021-05-25 8:25 ` Dietmar Eggemann
2021-05-25 9:30 ` Beata Michalska
2021-05-25 11:59 ` Dietmar Eggemann
2021-05-25 14:04 ` Beata Michalska
2021-05-24 10:16 ` [PATCH v5 3/3] sched/doc: Update the CPU capacity asymmetry bits Beata Michalska
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