linux-kernel - Re: RFC: Ideal Adaptive Spinning Conditions

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Message-ID: <4BB4C566.8060308@redhat.com>
Date:	Thu, 01 Apr 2010 19:10:14 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Darren Hart <dvhltc@...ibm.com>
CC:	"lkml, " <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Sven-Thorsten Dietrich <sdietrich@...ell.com>,
	Peter Morreale <pmorreale@...ell.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Chris Mason <chris.mason@...cle.com>
Subject: Re: RFC: Ideal Adaptive Spinning Conditions

On 04/01/2010 06:54 PM, Darren Hart wrote:
>> A lock(); unlock(); loop spends most of its time with the lock held 
>> or contended.  Can you something like this:
>>
>>
>>    lock();
>>    for (i = 0; i < 1000; ++i)
>>         asm volatile ("" : : : "memory");
>>    unlock();
>>    for (i = 0; i < 10000; ++i)
>>         asm volatile ("" : : : "memory");
>
>
>
> Great idea. I'll be doing a more rigorous investigation on this of 
> course, but I thought I'd share the results of just dumping this into 
> the testcase:
>
> # ./futex_lock -i10000000
> futex_lock: Measure FUTEX_LOCK operations per second
>     Arguments: iterations=10000000 threads=256 adaptive=0
> Result: 420 Kiter/s
> lock calls:      9999872
> lock syscalls:   665824 (6.66%)
> unlock calls:    9999872
> unlock syscalls: 861240 (8.61%)
>
> # ./futex_lock -a -i10000000
> futex_lock: Measure FUTEX_LOCK operations per second
>     Arguments: iterations=10000000 threads=256 adaptive=1
> Result: 426 Kiter/s
> lock calls:      9999872
> lock syscalls:   558787 (5.59%)
> unlock calls:    9999872
> unlock syscalls: 603412 (6.03%)
>
> This is the first time I've seen adaptive locking have an advantage! 
> The second set of runs showed a slightly greater advantage. Note that 
> this was still with spinners being limited to one.

Question - do all threads finish at the same time, or wildly different 
times?

-- 
error compiling committee.c: too many arguments to function

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