Re: [PATCH v2] bit_spinlock: introduce smp_cond_load_relaxed

[Peter Zijlstra]

On Tue, Nov 06, 2018 at 08:33:56PM +0800, Gao Xiang wrote:
> Hi Peter,
> 
> On 2018/11/6 20:27, Peter Zijlstra wrote:
> > On Tue, Nov 06, 2018 at 07:36:41PM +0800, Gao Xiang wrote:
> >> IMO, to use wrapped up function for the detailed scenario could be better than
> >> open-coded all the time (eg. do cpu_relax(); while(...)) since it could be
> >> optimizated even more for the specific architecture...
> > That's the whole point though; if this actually matters, you're doing it
> > wrong.
> 
> I cannot fully understand your point...Sorry about my English...
> 
> To the point, you mean it is much better to fix it as Will suggested before or
> leave the matter as it is since the performance of bit_spinlock itself doesn't matter?

Right, bit-spinlocks are terrible when contended. If the contended
behaviour of bit-spinlocks start to matter, you've lost already.