Re: [PATCH v6 00/11] locking/rwsem: Rework rwsem-xadd & enable new rwsem features

[Peter Zijlstra]

On Wed, Oct 11, 2017 at 02:01:51PM -0400, Waiman Long wrote:
>   # of Patches		   Reader 		  Writer
>     Applied		Locking Rate		Locking Rate
>   ------------		------------		------------
> 	0	5,155/    5,155/    5,155    5,154/248,852/346,281
> 	7	5,696/    5,697/    5,698  113,500/215,826/320,872
> 	8	4,827/    5,047/    5,215    4,826/176,797/284,069
> 	9     211,276/  509,712/1,134,007    4,894/221,839/246,818
>        11     884,513/1,043,989/1,252,533    9,604/ 11,105/ 25,225
> 
> It can be seen that rwsem changes from writer-preferring to
> reader-preferring.

A bit radically so, you almost starve the writers there.