On 09/11/2018 06:13 PM, Dave Chinner wrote: > On Tue, Sep 11, 2018 at 03:18:26PM -0400, Waiman Long wrote: >> Because the accounting of nr_dentry_negative depends on whether a dentry >> is a negative one or not, branch instructions are introduced to handle >> the accounting conditionally. That may potentially slow down the task >> by a noticeable amount if that introduces sizeable amount of additional >> branch mispredictions. >> >> To avoid that, the accounting code is now modified to use conditional >> move instructions instead, if supported by the architecture. > I think this is a case of over-optimisation. It makes the code > harder to read for extremely marginal benefit, and if we ever need > to add any more code for negative dentries in these paths the first > thing we'll have to do is revert this change. > > Unless you have numbers demonstrating that it's a clear performance > improvement, then NACK for this patch. > > Cheers, > > Dave. Yes, this is an optimization. Unfortunately I don't have any performance number as I had not seen any significant performance difference outside of the noise range with these set of changes. I am not fine with not taking this patch. Cheers, Longman
