Dave Hansen <dave.hansen@xxxxxxxxx> writes: > On 5/3/22 10:14, Alistair Popple wrote: >> I would certainly be interested in figuring out how HW could provide some sort >> of heatmap to identify which pages are hot and which processing unit is using >> them. Currently for these systems users have to manually assign memory policy to >> get any reasonable performance, both to disable NUMA balancing and make sure >> memory is allocated on the right node. > > Autonuma-induced page faults are a total non-starter for lots of > workloads, even ignoring GPUs. Basically anyone who is latency > sensitive stays far, far away from autonuma. > > As for improving on page faults for data collection... > > *Can* hardware provide this information? Definitely. > > Have hardware vendors been motivated enough to add hardware to do this? > Nope, not yet. Not entirely true. The GPUs on POWER9 have performance counters capable of collecting this kind of information for memory accessed from the GPU. I will admit though that sadly most people probably don't have a P9 sitting under their desk :) For various reasons these counters weren't exposed to the kernel but that's something I would like to work on fixing. > Do you know anyone that works for any hardware companies? ;) Maybe ;) > Seriously, though. Folks at Intel _are_ thinking about this problem. > I'm hoping we have hardware some day to help lend a hand. The more > hardware vendors that do this, the more likely it is that we'll have > good kernel code to consume data from the hardware. Agreed.
