Re: [PATCH 3/3] WorkStruct: Use direct assignment rather than cmpxchg()

[David Howells]

Andrew Morton <akpm@xxxxxxxx> wrote:

> and we can assume (and ensure) that a failing test_and_set_bit() will not
> write to the affected word at all.

You may not assume that; and indeed that is not so in the generic
spinlock-based bitops or ARM pre-v6 or PA-RISC or sparc32 or ...

Remember: if you have to put a conditional jump in there, it's going to fail
one way or the other a certain percentage of the time, and that's going to
cause a pipeline stall, and these ops are used quite a lot.

OTOH, I don't know that the stall would be that bad since the spin_lock and
spin_unlock may cause a stall anyway.

David
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