linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Valentin Schneider <valentin.schneider@arm.com>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	lizefan@huawei.com, tj@kernel.org, hannes@cmpxchg.org,
	mingo@kernel.org, peterz@infradead.org,
	vincent.guittot@linaro.org, Dietmar.Eggemann@arm.com,
	morten.rasmussen@arm.com, qperret@google.com,
	stable@vger.kernel.org
Subject: Re: [PATCH v4 1/2] sched/topology: Don't try to build empty sched domains
Date: Thu, 31 Oct 2019 18:23:12 +0100	[thread overview]
Message-ID: <3752bca9-a670-f415-4aaa-e8ff75ea6fcc@arm.com> (raw)
In-Reply-To: <20191031162334.GA18570@blackbody.suse.cz>

Hi Michal,

On 31/10/2019 17:23, Michal Koutný wrote:
> On Wed, Oct 23, 2019 at 04:37:44PM +0100, Valentin Schneider <valentin.schneider@arm.com> wrote:
>> Prevent generate_sched_domains() from returning empty cpumasks, and add
>> some assertion in build_sched_domains() to scream bloody murder if it
>> happens again.
> Good catch. It makes sense to prune the empty domains in
> generate_sched_domains already.
> 
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index c52bc91f882b..c87ee6412b36 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -798,7 +798,8 @@ static int generate_sched_domains(cpumask_var_t **domains,
>>  		    cpumask_subset(cp->cpus_allowed, top_cpuset.effective_cpus))
>>  			continue;
>>  
>> -		if (is_sched_load_balance(cp))
>> +		if (is_sched_load_balance(cp) &&
>> +		    !cpumask_empty(cp->effective_cpus))
>>  			csa[csn++] = cp;
> If I didn't overlook anything, cp->effective_cpus can contain CPUs
> exluded by housekeeping_cpumask(HK_FLAG_DOMAIN) later, i.e. possibly
> still returning domains with empty cpusets.
> 
> I'd suggest moving the emptiness check down into the loop where domain
> cpumasks are ultimately constructed.
> 

Ah, wasn't aware of this - thanks for having a look!

I think I need to have the check before the final cpumask gets built,
because at this point the cpumask array is already built and it's handed
off directly to the sched domain rebuild.

Do you reckon the following would work? 

----8<----
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index c87ee6412b36..e4c10785dc7c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -798,8 +798,14 @@ static int generate_sched_domains(cpumask_var_t **domains,
 		    cpumask_subset(cp->cpus_allowed, top_cpuset.effective_cpus))
 			continue;
 
+		/*
+		 * Skip cpusets that would lead to an empty sched domain.
+		 * That could be because effective_cpus is empty, or because
+		 * it's only spanning CPUs outside the housekeeping mask.
+		 */
 		if (is_sched_load_balance(cp) &&
-		    !cpumask_empty(cp->effective_cpus))
+		    cpumask_intersects(cp->effective_cpus,
+				       housekeeping_cpumask(HK_FLAG_DOMAIN)))
 			csa[csn++] = cp;
 
 		/* skip @cp's subtree if not a partition root */

  reply	other threads:[~2019-10-31 17:23 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-23 15:37 [PATCH v4 0/2] sched/topology: Asymmetric topologies fixes Valentin Schneider
2019-10-23 15:37 ` [PATCH v4 1/2] sched/topology: Don't try to build empty sched domains Valentin Schneider
2019-10-24 16:19   ` Dietmar Eggemann
2019-10-24 16:45     ` Valentin Schneider
2019-10-29  9:52   ` [tip: sched/urgent] " tip-bot2 for Valentin Schneider
2019-10-31 16:23   ` [PATCH v4 1/2] " Michal Koutný
2019-10-31 17:23     ` Valentin Schneider [this message]
2019-11-01 10:08       ` Michal Koutný
2019-10-23 15:37 ` [PATCH v4 2/2] sched/topology: Allow sched_asym_cpucapacity to be disabled Valentin Schneider
2019-10-29  9:52   ` [tip: sched/urgent] " tip-bot2 for Valentin Schneider

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=3752bca9-a670-f415-4aaa-e8ff75ea6fcc@arm.com \
    --to=valentin.schneider@arm.com \
    --cc=Dietmar.Eggemann@arm.com \
    --cc=cgroups@vger.kernel.org \
    --cc=hannes@cmpxchg.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=lizefan@huawei.com \
    --cc=mingo@kernel.org \
    --cc=mkoutny@suse.com \
    --cc=morten.rasmussen@arm.com \
    --cc=peterz@infradead.org \
    --cc=qperret@google.com \
    --cc=stable@vger.kernel.org \
    --cc=tj@kernel.org \
    --cc=vincent.guittot@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).