Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH 3/3] WorkStruct: Use direct assignment rather than cmpxchg() | Date | Thu, 07 Dec 2006 20:06:39 +0000 |
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Andrew Morton <akpm@osdl.org> 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.
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