Re: [RFC][PATCH 0/7] locking: qspinlock

[Waiman Long]

On 03/11/2014 06:45 AM, Ingo Molnar wrote:
> * Peter Zijlstra<peterz@xxxxxxxxxxxxx>  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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