On Sat, Dec 21, 2024 at 01:18:04PM +0800, Huang, Ying wrote: > Gregory Price <gourry@xxxxxxxxxx> writes: > > > > > Single-reader DRAM: ~16.0-16.4s > > Single-reader CXL (after demotion): ~16.8-17s > > The difference is trivial. This makes me thought that why we need this > patchset? > That's 3-6% performance in this contrived case. We're working to testing a real workload we know suffers from this problem as it is long-running. Should be early in the new year hopefully. > > Next we turned promotion on with only a single reader running. > > > > Before promotions: > > Node 0 MemFree: 636478112 kB > > Node 0 FilePages: 59009156 kB > > Node 1 MemFree: 250336004 kB > > Node 1 FilePages: 14979628 kB > > Why are there some many file pages on node 1 even if there're a lot of > free pages on node 0? You moved some file pages from node 0 to node 1? > This was explicit and explained in the test notes: First we ran with promotion disabled to show consistent overhead as a result of forcing a file out to CXL memory. We first ran a single reader to see uncontended performance, launched many readers to force demotions, then dropped back to a single reader to observe. The goal here was to simply demonstrate functionality and stability. > > After promotions: > > Node 0 MemFree: 632267268 kB > > Node 0 FilePages: 72204968 kB > > Node 1 MemFree: 262567056 kB > > Node 1 FilePages: 2918768 kB > > > > Single-reader (after_promotion): ~16.5s This represents a 2.5-6% speedup depending on the spread. > > > > numa_migrate_prep: 93 - time(3969867917) count(42576860) > > migrate_misplaced_folio_prepare: 491 - time(3433174319) count(6985523) > > migrate_misplaced_folio: 1635 - time(11426529980) count(6985523) > > > > Thoughts on a good throttling heuristic would be appreciated here. > > We do have a throttle mechanism already, for example, you can used > > $ echo 100 > /proc/sys/kernel/numa_balancing_promote_rate_limit_MBps > > to rate limit the promotion throughput under 100 MB/s for each DRAM > node. > Can easily piggyback on that, just wasn't sure if overloading it was an acceptable idea. Although since that promotion rate limit is also per-task (as far as I know, will need to read into it a bit more) this is probably fine. ~Gregory
