On Tue, 3 Apr 2018, Thomas Gleixner wrote: > On Thu, 29 Mar 2018, Vikas Shivappa wrote: > You said above: > > > This may lead to confusion in scenarios below: > > Reading the blurb after that creates even more confusion than being > helpful. > > First of all this information should not be under the section 'Memory > bandwidth in MB/s'. > > Also please write bandwidth. The weird acronym b/w (band per width???) is > really not increasing legibility. > > What you really want is a general section about memory bandwidth allocation > where you explain the technical background in purely technical terms w/o > fairy tale mode. Technical descriptions have to be factual and not > 'could/may/would'. > > If I decode the above correctly then the current percentage based > implementation was buggy from the very beginning in several ways. > > Now the obvious question which is in no way answered by the cover letter is > why the current percentage based implementation cannot be fixed and we need > some feedback driven magic to achieve that. I assume you spent some brain > cycles on that question, so it would be really helpful if you shared that. > > If I understand it correctly then the problem is that the throttling > mechanism is per core and affects the L2 external bandwidth. > > Is this really per core? What about hyper threads. Both threads have that > MSR. How is that working? > > The L2 external bandwidth is higher than the L3 external bandwidth. > > Is there any information available from CPUID or whatever source which > allows us to retrieve the bandwidth ratio or the absolute maximum > bandwidth per level? > > What's also missing from your explanation is how that feedback loop behaves > under different workloads. > > Is this assuming that the involved threads/cpus actually try to utilize > the bandwidth completely? > > What happens if the threads/cpus are only using a small set because they > are idle or their computations are mostly cache local and do not need > external bandwidth? Looking at the implementation I don't see how that is > taken into account.
Forgot to mention the following: The proposed new interface has no upper limit. The existing percentage based implementation has at least some notion of limit and scale; not really helpful either because of the hardware implementation. but I How is the poor admin supposed to configure that new thing without knowing what the actual hardware limits are in the first place? Thanks, tglx