On 01/09/2019 01:52 PM, Matthew Wilcox wrote: > On Wed, Jan 09, 2019 at 01:37:23PM -0500, Waiman Long wrote: >> On 01/09/2019 01:24 PM, Matthew Wilcox wrote: >>> Did you even try just using the general purpose infrastructure that's >>> in place? If that shows a performance problem _then_ it's time to make >>> this special snowflake just a little more special. Not before. >> I have looked into the percpu counter code. There are two aspects that I >> don't like to introduce to the interrupt handler's code path for >> updating the counts. >> >> 1) There is a raw spinlock in the percpu_counter structure that may need >> to be acquired in the update path. This can be a performance drag >> especially if lockdep is enabled. >> >> 2) The percpu_counter structure is 40 bytes in size on 64-bit systems >> compared with just 8 bytes for the percpu count pointer and an >> additional 4 bytes that I introduced in patch 2. With thousands of irq >> descriptors, it can consume quite a lot more memory. Memory consumption >> was a point that you brought up in one of your previous mails. > Then _argue that_. Don't just go off and do something random without > explaining to the rest of us why we're wrong. Sorry about that. I should have included that in the cover-letter. Cheers, Longman
