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Re: [PATCH] hppa: Optimize atomic_compare_and_exchange_val_acq

On 09/22/2016 05:38 PM, Helge Deller wrote:
> On 22.09.2016 22:37, Carlos O'Donell wrote:
>> On 09/22/2016 10:14 AM, John David Anglin wrote:
>>> The attached patch replaces the conditional branch tests in
>>> atomic_compare_and_exchange_val_acq with conditional instruction
>>> nullification. This avoids the stalls associated with conditional
>>> branches and the resulting code is shorter. There are no branches in
>>> the fast path when the operation is successful.
>> Does this really make a measurable difference? The light-weight-syscall
>> is probably the most costly part of this entire operation.
>> If you can show there is a measurable difference I would be willing
>> to accept the removal of the deadlock looping (it becomes a SIGILL
>> and you have to look at the core file).
> I'm with Dave that the removal of the deadlock looping is OK.
> There is no production kernel in real-life (e.g. Debian kernels) which
> return EDEADLOCK, because in the Linux kernel we have completely disabled
> the LWS debugging by default (ENABLE_LWS_DEBUG=0) and as such I see
> no kernel code path where EDEADLOCK can be returned.



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