On Mon, May 21, 2018 at 09:51:19PM -0600, Jens Axboe wrote: > On May 21, 2018, at 9:47 PM, Ming Lei <ming.lei@xxxxxxxxxx> wrote: > > > >> On Mon, May 21, 2018 at 09:16:33PM -0600, Jens Axboe wrote: > >>> On 5/21/18 8:49 PM, Ming Lei wrote: > >>>> On Mon, May 21, 2018 at 05:11:31PM -0600, Keith Busch wrote: > >>>> This patch simplifies the timeout handling by relying on the request > >>>> reference counting to ensure the iterator is operating on an inflight > >>> > >>> The reference counting isn't free, what is the real benefit in this way? > >> > >> Neither is the current scheme and locking, and this is a hell of a lot > >> simpler. I'd get rid of the kref stuff and just do a simple > >> atomic_dec_and_test(). Most of the time we should be uncontended on > >> that, which would make it pretty darn cheap. I'd be surprised if it > >> wasn't better than the current alternatives. > > > > The explicit memory barriers by atomic_dec_and_test() isn't free. > > I’m not saying it’s free. Neither is our current synchronization. > > > Also the double completion issue need to be fixed before discussing > > this approach further. > > Certainly. Also not saying that the current patch is perfect. But it’s a lot more palatable than the alternatives, hence my interest. And I’d like for this issue to get solved, we seem to be a bit stuck atm. > It may not be something we are stuck at, and seems no alternatives for this patchset. It is a new requirement from NVMe, and Keith wants driver to complete timed-out request in .timeout(). We never support that before for both mq and non-mq code path. Thanks, Ming
