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. > Do I know about anybody requiring that now? No! But we should really > test the proposed interface for potential future extensions. If such an > extension is not reasonable and/or we can achieve that by different > means then great. -- Best Regards, Huang, Ying
