linux-kernel - Re: [Patch] Idle balancer: cache align nohz structure to improve idle load balancing scalability

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

Message-ID: <CABeCy1a20npBt=4ee38zLH+6Fi7nfASd0dL3od6pOccV=LJDkA@mail.gmail.com>
Date:	Thu, 20 Oct 2011 05:26:32 -0700
From:	Venki Pallipadi <venki@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Tim Chen <tim.c.chen@...ux.intel.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [Patch] Idle balancer: cache align nohz structure to improve idle
 load balancing scalability

On Wed, Oct 19, 2011 at 9:24 PM, Andi Kleen <andi@...stfloor.org> wrote:
> Tim Chen <tim.c.chen@...ux.intel.com> writes:
>>   */
>>  static struct {
>> -     atomic_t load_balancer;
>> -     atomic_t first_pick_cpu;
>> -     atomic_t second_pick_cpu;
>> -     cpumask_var_t idle_cpus_mask;
>> +     atomic_t load_balancer ____cacheline_aligned;
>> +     atomic_t first_pick_cpu ____cacheline_aligned;
>> +     atomic_t second_pick_cpu ____cacheline_aligned;
>> +     cpumask_var_t idle_cpus_mask ____cacheline_aligned;
>
> On large configs idle_cpu_masks may be allocated.  May need
> more changes to tell the allocator to cache align/pad too?
>

An alternate approach is to split this struct per node/socket and do
the nohz idle balancing logic at that level. That should be more
scalable in terms of nohz balancing (ensure one CPU wont be doing nohz
balancing for huge number of idle CPUs). I had looked at that approach
couple of years earlier and couldn't measure that much of a gain. May
be it is time to revisit that with increased core count.

Thanks,
Venki
--
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/