On Thu 02-11-23 14:21:49, Huang, Ying wrote: > Michal Hocko <mhocko@xxxxxxxx> writes: > > > On Tue 31-10-23 12:22:16, Johannes Weiner wrote: > >> On Tue, Oct 31, 2023 at 04:56:27PM +0100, Michal Hocko wrote: > > [...] > >> > Is there any specific reason for not having a new interleave interface > >> > which defines weights for the nodemask? Is this because the policy > >> > itself is very dynamic or is this more driven by simplicity of use? > >> > >> A downside of *requiring* weights to be paired with the mempolicy is > >> that it's then the application that would have to figure out the > >> weights dynamically, instead of having a static host configuration. A > >> policy of "I want to be spread for optimal bus bandwidth" translates > >> between different hardware configurations, but optimal weights will > >> vary depending on the type of machine a job runs on. > > > > I can imagine this could be achieved by numactl(8) so that the process > > management tool could set this up for the process on the start up. Sure > > it wouldn't be very dynamic after then and that is why I was asking > > about how dynamic the situation might be in practice. > > > >> That doesn't mean there couldn't be usecases for having weights as > >> policy as well in other scenarios, like you allude to above. It's just > >> so far such usecases haven't really materialized or spelled out > >> concretely. Maybe we just want both - a global default, and the > >> ability to override it locally. Could you elaborate on the 'get what > >> you pay for' usecase you mentioned? > > > > This is more or less just an idea that came first to my mind when > > hearing about bus bandwidth optimizations. I suspect that sooner or > > later we just learn about usecases where the optimization function > > maximizes not only bandwidth but also cost for that bandwidth. Consider > > a hosting system serving different workloads each paying different > > QoS. > > I don't think pure software solution can enforce the memory bandwidth > allocation. For that, we will need something like MBA (Memory Bandwidth > Allocation) as in the following URL, > > https://www.intel.com/content/www/us/en/developer/articles/technical/introduction-to-memory-bandwidth-allocation.html > > At lease, something like MBM (Memory Bandwidth Monitoring) as in the > following URL will be needed. > > https://www.intel.com/content/www/us/en/developer/articles/technical/introduction-to-memory-bandwidth-monitoring.html > > The interleave solution helps the cooperative workloads only. Enforcement is an orthogonal thing IMO. We are talking about a best effort interface. -- Michal Hocko SUSE Labs
