Re: [PATCH 0/2] jump label: 2.6.38 updates

[Segher Boessenkool]

>> What CPU family are we talking about here?  For cache coherent CPUs,
>> cache coherence really is supposed to work, even for mixed atomic and
>> non-atomic instructions to the same variable.
>
> I'm really curious to know which CPU families too. I've used git blame
> to see where these lwz/stw instructions were added to powerpc, and it
> points to:
>
> commit 9f0cbea0d8cc47801b853d3c61d0e17475b0cc89

> So let's ping the relevant people to see if there was any reason for
> making these atomic read/set operations different from other
> architectures in the first place.

lwz is a simple 32-bit load.  On PowerPC, such a load is guaranteed
to be atomic (except some unaligned cases).  stw is similar, for stores.
These are the normal insns, not ll/sc or anything.

At the time, volatile tricks were used to make the accesses atomic; this
patch changed that.  Result is (or should be!) better code generation.

Is there a problem with it?


Segher

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