linux-kernel - Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount

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Date:	Wed, 04 Sep 2013 22:35:40 -0400
From:	Waiman Long <waiman.long@...com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jeff Layton <jlayton@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount

On 09/04/2013 05:34 PM, Linus Torvalds wrote:
> On Wed, Sep 4, 2013 at 12:25 PM, Waiman Long<waiman.long@...com>  wrote:
>> Yes, the perf profile was taking from an 80-core machine. There isn't any
>> scalability issue hiding for the short workload on an 80-core machine.
>>
>> However, I am certain that more may pop up when running in an even larger
>> machine like the prototype 240-core machine that our team has been testing
>> on.
> Sure. Please let us know, I think it's going to be interesting to see
> what that shows.
>
> SGI certainly did much larger machines, but their primary target
> tended to be all user space, so they had things like "tons of
> concurrent page faults in the same process" rather than filename
> lookup or the tty layer.
>
>                  Linus

I think SGI is more focus on compute-intensive workload. HP is more 
focus on high-end commercial workload like SAP HANA. Below was a sample 
perf profile of the high-systime workload on a 240-core prototype 
machine (HT off) with 3.10-rc1 kernel with my lockref and seqlock patches:

      9.61%    3382925          swapper  [kernel.kallsyms]         [k] 
_raw_spin_lock
                        |--59.90%-- rcu_process_callbacks
                        |--19.41%-- load_balance
                        |--9.58%-- rcu_accelerate_cbs
                        |--6.70%-- tick_do_update_jiffies64
                        |--1.46%-- scheduler_tick
                        |--1.17%-- sched_rt_period_timer
                        |--0.56%-- perf_adjust_freq_unthr_context
                         --1.21%-- [...]

      6.34%         99            reaim  [kernel.kallsyms]         [k] 
_raw_spin_lock
                          |--73.96%-- load_balance
                          |--11.98%-- rcu_process_callbacks
                          |--2.21%-- __mutex_lock_slowpath
                          |--2.02%-- rcu_accelerate_cbs
                          |--1.95%-- wake_up_new_task
                          |--1.70%-- scheduler_tick
                          |--1.67%-- xfs_alloc_log_agf
                          |--1.24%-- task_rq_lock
                          |--1.15%-- try_to_wake_up
                           --2.12%-- [...]

      5.39%          2            reaim  [kernel.kallsyms]         [k] 
_raw_spin_lock_irqsave
                          |--95.08%-- rwsem_wake
                          |--1.80%-- rcu_process_callbacks
                          |--1.03%-- prepare_to_wait
                          |--0.59%-- __wake_up
                           --1.50%-- [...]

      2.28%          1            reaim  [kernel.kallsyms]         [k] 
_raw_spin_lock_irq
                          |--90.56%-- rwsem_down_write_failed
                          |--9.25%-- __schedule
                           --0.19%-- [...]

Longman
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