linux-kernel - Re: [PATCH v2 0/4] ipc: reduce ipc lock contention

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Date:	Tue, 05 Mar 2013 23:13:32 -0800
From:	Davidlohr Bueso <davidlohr.bueso@...com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Emmanuel Benisty <benisty.e@...il.com>,
	"Vinod, Chegu" <chegu_vinod@...com>,
	"Low, Jason" <jason.low2@...com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>, aquini@...hat.com,
	Michel Lespinasse <walken@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Larry Woodman <lwoodman@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 0/4] ipc: reduce ipc lock contention

On Tue, 2013-03-05 at 07:40 -0800, Linus Torvalds wrote:
> On Tue, Mar 5, 2013 at 1:35 AM, Davidlohr Bueso <davidlohr.bueso@...com> wrote:
> >
> > The following set of patches are based on the discussion of holding the
> > ipc lock unnecessarily, such as for permissions and security checks:
> 
> Ok, looks fine from a quick look (but then, so did your previous patch-set ;)
> 
> You still open-code the spinlock in at least a few places (I saw
> sem_getref), but I still don't care deeply.
> 
> >> 2) While on an Oracle swingbench DSS (data mining) workload the
> > improvements are not as exciting as with Rik's benchmark, we can see
> > some positive numbers. For an 8 socket machine the following are the
> > percentages of %sys time incurred in the ipc lock:
> 
> Ok, I hoped for it being more noticeable. Since that benchmark is less
> trivial than Rik's, can you do a perf record -fg of it and give a more
> complete picture of what the kernel footprint is - and in particular
> who now gets that ipc lock function? Is it purely semtimedop, or what?
> Look out for inlining - ipc_rcu_getref() looks like it would be
> inlined, for example.
> 
> It would be good to get a "top twenty kernel functions" from the
> profile, along with some call data on where the lock callers are.. I
> know that Rik's benchmark *only* had that one call-site, I'm wondering
> if the swingbench one has slightly more complex behavior...

For a 400 user workload (the kernel functions remain basically the same
for any amount of users):

    17.86%           oracle  [kernel.kallsyms]   [k] _raw_spin_lock                             
     8.46%          swapper  [kernel.kallsyms]   [k] intel_idle                                 
     5.51%           oracle  [kernel.kallsyms]   [k] try_atomic_semop                           
     5.05%           oracle  [kernel.kallsyms]   [k] update_sd_lb_stats                         
     2.81%           oracle  [kernel.kallsyms]   [k] tg_load_down                               
     2.41%          swapper  [kernel.kallsyms]   [k] update_blocked_averages                    
     2.38%           oracle  [kernel.kallsyms]   [k] idle_cpu                                   
     2.37%          swapper  [kernel.kallsyms]   [k] native_write_msr_safe                      
     2.28%           oracle  [kernel.kallsyms]   [k] update_cfs_rq_blocked_load                 
     1.84%           oracle  [kernel.kallsyms]   [k] update_blocked_averages                    
     1.79%           oracle  [kernel.kallsyms]   [k] update_queue                               
     1.73%          swapper  [kernel.kallsyms]   [k] update_cfs_rq_blocked_load                 
     1.29%           oracle  [kernel.kallsyms]   [k] native_write_msr_safe                      
     1.07%             java  [kernel.kallsyms]   [k] update_sd_lb_stats                         
     0.91%          swapper  [kernel.kallsyms]   [k] poll_idle                                  
     0.86%           oracle  [kernel.kallsyms]   [k] try_to_wake_up                             
     0.80%             java  [kernel.kallsyms]   [k] tg_load_down                               
     0.72%           oracle  [kernel.kallsyms]   [k] load_balance                               
     0.67%           oracle  [kernel.kallsyms]   [k] __schedule                                 
     0.67%           oracle  [kernel.kallsyms]   [k] cpumask_next_and                           

Digging into the _raw_spin_lock call:

 17.86%           oracle  [kernel.kallsyms]   [k] _raw_spin_lock                            
                     |
                     --- _raw_spin_lock
                        |          
                        |--49.55%-- sys_semtimedop
                        |          |          
                        |          |--77.41%-- system_call
                        |          |          semtimedop
                        |          |          skgpwwait
                        |          |          ksliwat
                        |          |          kslwaitctx


Thanks,
Davidlohr


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