Re: [PATCH] locking/rwsem: Make owner store task pointer of last owning reader

[Davidlohr Bueso]

On Mon, 10 Sep 2018, Waiman Long wrote:

> One major issue with a combined count/owner is that we may have to use
> cmpxchg for reader lock which will certainly impact reader-heavy
> workloads. I have also thought about ways to compress the task pointer
> address so that it can use fewer bits and leave the rests for reader
> count. It is probably doable on 64-bit systems, but likely not on 32-bit
> system given that there are less bits to play around.

Yeah we've discussed this before. As a cleanup it would obviously be good,
but I fear about raw performance loss when using cmpxchg instead of xadd.

Thanks,
Davidlohr