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SubjectRe: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter
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> On Nov 21, 2019, at 11:56 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Thu, Nov 21, 2019 at 09:51:03AM -0800, Andy Lutomirski wrote:
>
>> Can we really not just change the lock asm to use 32-bit accesses for
>> set_bit(), etc? Sure, it will fail if the bit index is greater than
>> 2^32, but that seems nuts.
>
> There are 64bit architectures that do exactly that: Alpha, IA64.
>
> And because of the byte 'optimization' from x86 we already could not
> rely on word atomicity (we actually play games with multi-bit atomicity
> for PG_waiters and clear_bit_unlock_is_negative_byte).

I read a couple pages of the paper you linked and I didn’t spot what you’re talking about as it refers to x86. What are the relevant word properties of x86 bitops or the byte optimization?
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