linux-kernel - Re: [RFC] sched: Limit idle_balance() when it is being used too frequently

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]

Message-ID: <1374261318.1830.6.camel@j-VirtualBox>
Date:	Fri, 19 Jul 2013 12:15:18 -0700
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>, Alex Shi <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Mel Gorman <mgorman@...e.de>, aswin@...com,
	scott.norton@...com, chegu_vinod@...com
Subject: Re: [RFC] sched: Limit idle_balance() when it is being used too
 frequently

On Fri, 2013-07-19 at 20:37 +0200, Peter Zijlstra wrote:
> On Thu, Jul 18, 2013 at 12:06:39PM -0700, Jason Low wrote:
> 
> > N = 1
> > -----
> > 19.21%  reaim  [k] __read_lock_failed                     
> > 14.79%  reaim  [k] mspin_lock                             
> > 12.19%  reaim  [k] __write_lock_failed                    
> > 7.87%   reaim  [k] _raw_spin_lock                          
> > 2.03%   reaim  [k] start_this_handle                       
> > 1.98%   reaim  [k] update_sd_lb_stats                      
> > 1.92%   reaim  [k] mutex_spin_on_owner                     
> > 1.86%   reaim  [k] update_cfs_rq_blocked_load              
> > 1.14%   swapper  [k] intel_idle                              
> > 1.10%   reaim  [.] add_long                                
> > 1.09%   reaim  [.] add_int                                 
> > 1.08%   reaim  [k] load_balance                            
> 
> But but but but.. wth is causing this? The only thing we do more of with
> N=1 is idle_balance(); where would that cause __{read,write}_lock_failed
> and or mspin_lock() contention like that.
> 
> There shouldn't be a rwlock_t in the entire scheduler; those things suck
> worse than quicksand.
> 
> If, as Rik thought, we'd have more rq->lock contention, then I'd
> expected _raw_spin_lock to be up highest.

For this particular fserver workload, that mutex was acquired in the
function calls from ext4_orphan_add() and ext4_orphan_del(). Those read
and write lock calls were from start_this_handle(). 

Although these functions are not called within the idle_balance() code
path, update_sd_lb_stats(), tg_load_down(), idle_cpu(), spin_lock(),
ect... increases the time spent in the kernel and that appears to be
indirectly causing more time to be spent acquiring those other kernel
locks.

Thanks,
Jason



--
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/