Re: [parisc-linux] [RFC] Alternative implementation of glibc spinlocks

[Randolph Chung <randolph@tausq.org>]

Please reply on list.

> 1) Your free-listing of locks does not appear to be thread safe;
>     I.E: Protected from concurrent changes.
> 
> But then, perhaps my mind is going and I just did not
> read the code closely enough.

They are protected by a spinlock.

> 2) How about an alternative implementation?
> Based on 4,096 byte pages;
> 
> Using the find_[first|last]_[zero|one] asm routines;
> 
> As I recall, they only go to 64 bits currently but only
> require 3 instructions per binary radix (add 6 instructions
> for 256 bits);
> 
> First 16 bytes of the page - your current header;
> Second 16 bytes of the page - bitmap of available locks;

Why do you need a bitmap?

> First bit of the bitmap represents the current header -
> use this to lock the page list (currently called free-list);
> 
> Second bit of the bitmap represents the bitmap -
> use this to lock the bitmap;

how do you use a bit to do locking?

> The remaining 254 bits/lock structures per page are usable.

randolph
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