On Wed, Jul 13, 2016 at 10:51:02PM +0200, Peter Zijlstra wrote: > On Wed, Jul 13, 2016 at 04:39:44PM -0400, Tejun Heo wrote: > So, IIRC, the trade-off is a full memory barrier in read_lock and > read_unlock() vs sync_sched() in write. > > Full memory barriers are expensive and while the combined cost might > well exceed the cost of the sync_sched() it doesn't suffer the latency > issues.
Given the way read side is used for percpu_rwsem, full memory barrier on reader side shouldn't matter at all. The paths are not *that* hot. > Not sure if we can frob the two in a single codebase, but I can have a > poke if Oleg or Paul doesn't beat me to it. At the simplest, it can be rwsem equivalence of lglock. -- tejun
