On Wed, Oct 11, 2017 at 02:58:02PM -0400, Waiman Long wrote: > On 10/11/2017 02:40 PM, Peter Zijlstra wrote: > > So I implemented rwsem-mutex (also qrwlock based) that puts > > > > (unsigned long)current | RWSEM_WRITER > > > > in the atomic_long_t rw_semaphore::owner field. The down-side is that > > you can't do fetch_add based __down_read, because that would clobber the > > pointer. The up-side is that we have a stable owner pointer (which is > > what I needed for PI like things). > > Without fetch_add for readers, it could lead to reduced performance for > reader heavy workloads. Yeah I know.. :-) > Are you trying to do a PI version of rwsem? It can work when the lock is > writer owned, but not when it is reader owned. Not classical PI; there's one of those in -rt btw: https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tree/kernel/locking/rwsem-rt.c?h=linux-4.11.y-rt I'm implementing proxy-execution (or rather, playing with it in a few spare moments here and there). But yes, it will only be able to boost write owners. But in order to make that happen I need the lock state and owner thing in the same field, like mutex. In any case, I'll try and have a look at these patches. -- To unsubscribe from this list: send the line "unsubscribe linux-alpha" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
