linux-kernel - Re: [RFC][PATCH 0/7] locking: qspinlock

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Date:	Tue, 11 Mar 2014 23:17:46 -0400
From:	Waiman Long <waiman.long@...com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>, arnd@...db.de,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	akpm@...ux-foundation.org, walken@...gle.com, andi@...stfloor.org,
	riel@...hat.com, paulmck@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org, oleg@...hat.com
Subject: Re: [RFC][PATCH 0/7] locking: qspinlock

On 03/11/2014 06:45 AM, Ingo Molnar wrote:
> * Peter Zijlstra<peterz@...radead.org>  wrote:
>
>> Hi Waiman,
>>
>> I promised you this series a number of days ago; sorry for the delay
>> I've been somewhat unwell :/
>>
>> That said, these few patches start with a (hopefully) simple and
>> correct form of the queue spinlock, and then gradually build upon
>> it, explaining each optimization as we go.
>>
>> Having these optimizations as separate patches helps twofold;
>> firstly it makes one aware of which exact optimizations were done,
>> and secondly it allows one to proove or disprove any one step;
>> seeing how they should be mostly identity transforms.
>>
>> The resulting code is near to what you posted I think; however it
>> has one atomic op less in the pending wait-acquire case for NR_CPUS
>> != huge. It also doesn't do lock stealing; its still perfectly fair
>> afaict.
>>
>> Have I missed any tricks from your code?
> Waiman, you indicated in the other thread that these look good to you,
> right? If so then I can queue them up so that they form a base for
> further work.
>
> It would be nice to have per patch performance measurements though ...
> this split-up structure really enables that rather nicely.
>
> Thanks,
>
> 	Ingo
As said by Peter, I haven't reviewed his change yet. The patch I am 
working on has an optimization that is similar to PeterZ's small NR_CPUS 
change. Except that I do a single atomic short integer write to switch 
the bits instead of 2 byte write. However, this code seems to have some 
problem working with the lockref code and I had panic happening in 
fs/dcache.c. So I am investigating that issue.

I am also trying to revise the PV support to be similar to what is 
currently done in the PV ticketlock code. That is why I am kind of 
silent this past week.

-Longman
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