linux-kernel - Re: [PATCH v2] sched: make update_sd_pick

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Mon, 28 Jul 2014 11:04:28 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Michael Neuling <mikey@...ling.org>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	jhladky@...hat.com, ktkhai@...allels.com,
	tim.c.chen@...ux.intel.com,
	Nicolas Pitre <nicolas.pitre@...aro.org>
Subject: Re: [PATCH v2] sched: make update_sd_pick_busiest return true on
 a busier sd

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 07/28/2014 04:23 AM, Vincent Guittot wrote:
> On 25 July 2014 21:32, Rik van Riel <riel@...hat.com> wrote:
>> Subject: sched: make update_sd_pick_busiest return true on a
>> busier sd
>> 
>> Currently update_sd_pick_busiest only identifies the busiest sd 
>> that is either overloaded, or has a group imbalance. When no sd
>> is imbalanced or overloaded, the load balancer fails to find the
>> busiest domain.
>> 
>> This breaks load balancing between domains that are not
>> overloaded, in the !SD_ASYM_PACKING case. This patch makes
>> update_sd_pick_busiest return true when the busiest sd yet is
>> encountered.
>> 
>> Behaviour for SD_ASYM_PACKING does not seem to match the
>> comment, but I have no hardware to test that so I have left the
>> behaviour of that code unchanged.
>> 
>> It is unclear what to do with the group_imb condition. Should
>> group_imb override a busier load? If so, should we fix
> 
> IMHO, group_imb should have a lower priority compared to
> overloaded group because it generates active migration whereas the
> use of overloaded group could solve the imbalance with normal
> migration Then, AFAICT, we already have a special way to compute
> imbalance when group_imb is set
> 
>> calculate_imbalance to return a sensible number when the
>> "busiest" node found has a below average load? We probably need
>> to fix calculate_imbalance anyway, to deal with an overloaded
>> group that happens to have a below average load...
>> 
>> Cc: mikey@...ling.org Cc: peterz@...radead.org Signed-off-by: Rik
>> van Riel <riel@...hat.com> --- kernel/sched/fair.c | 18
>> +++++++++++++----- 1 file changed, 13 insertions(+), 5
>> deletions(-)
>> 
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index
>> 45943b2..c96044f 100644 --- a/kernel/sched/fair.c +++
>> b/kernel/sched/fair.c @@ -5949,6 +5949,11 @@ static inline void
>> update_sg_lb_stats(struct lb_env *env, 
>> sgs->group_has_free_capacity = 1; }
>> 
>> +static bool group_overloaded(struct sg_lb_stats *sgs) +{ +
>> return sgs->sum_nr_running > sgs->group_capacity_factor; +} + 
>> /** * update_sd_pick_busiest - return 1 on busiest group * @env:
>> The load balancing environment. @@ -5957,7 +5962,7 @@ static
>> inline void update_sg_lb_stats(struct lb_env *env, * @sgs:
>> sched_group statistics * * Determine if @sg is a busier group
>> than the previously selected - * busiest group. + * busiest
>> group. * * Return: %true if @sg is a busier group than the
>> previously selected * busiest group. %false otherwise. @@
>> -5967,13 +5972,17 @@ static bool update_sd_pick_busiest(struct
>> lb_env *env, struct sched_group *sg, struct sg_lb_stats *sgs) { +
>> if (group_overloaded(sgs) &&
>> !group_overloaded(&sds->busiest_stat))
> 
> The 1st time you run update_sd_pick_busiest, group_capacity_factor
> and sum_nr_running of sds->busiest_stat are uninitialized.

Good point, init_sd_lb_stats only zeroes out a few fields.

I will fix this in the next version.

>> +               return true; +
> 
> IIUC your new test sequence, you haven't solved the following use
> case:

Fixed in the next version, with Peter's idea.

- -- 
All rights reversed
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

iQEcBAEBAgAGBQJT1mZ8AAoJEM553pKExN6DpPAH/A+a9Lbz/pV8uFGG3RRrs2gI
l8rhgtVLEM0uiDTDavB/D1GBnWcxfNbg6o/yF7dTXDA+sWltztZISi6dZ9JpEhww
0wK3rOD6t+VYpu6OaA2rIp2p2o12ou2d8ipjimjGf9gGD8i6vZiGOfTytsSateZH
X9pSQ5Tv63ES8m3DeLcXEy+YQVunyLD83aTwSpziBFKUGguttTvvqEx5MutxVQyA
Wx7hqX4VTR2oC3mS6djzK/hp0OmpZL4WKmnqUgjm11k0+UvBc1MnYE937CHixOdQ
GjfIgk+G8EGVucbKFfhgwrNFfemL4MXxSVxMMor1lMFt9yFKcwoSMRS40mcH+Rw=
=qENP
-----END PGP SIGNATURE-----
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/