Hello, Try #2 of the patches here. I sent earlier an RFC version against block/bio [1], and then an isolated patch for NVMe driver only [2]. After feedback from maintainers, I've reworked the patches again to block layer, this time to multiqueue support only. Once a blk-mq request is about to be dispatched to the driver layer, the PM QoS variables for active CPUs are tweaked based on configuration, and a timeout is launched as a delayed work that drops the PM QoS limits once the queue is idle. The mechanism is disabled by default, and only enabled once user activates it via the provided sysfs knobs. Some measurement data provided below as a reference for the results, measured with 'fio' on an Intel Icelake Xeon platform, with an extra NVMe card on the system. Both latency and bandwidth values are provided, to showcase that the latency is reduced and bandwidth is not impacted negatively due to overhead. C6 residency measurement is not very accurate in my test leading to somewhat glitchy result on its value (c6%). key: slat: start latency max, in us clat: completion latency max, in us lat: overall latency max, in us bw: min-avg-max bandwidth values c6%: c6 (deep idle) residency for the active CPU during the test cpu_lat_limit_us=10 (enabled) slat: 63, clat: 107, lat: 115, bw: 1177-1367-1397, c6%: 11.9 slat: 30, clat: 129, lat: 137, bw: 1196-1380-1409, c6%: 0.9 slat: 60, clat: 101, lat: 109, bw: 1193-1372-1407, c6%: 0.9 slat: 29, clat: 135, lat: 143, bw: 1184-1369-1398, c6%: 1.0 slat: 29, clat: 112, lat: 120, bw: 1188-1368-1397, c6%: 1.0 cpu_lat_limit_us=-1 (disabled) slat: 106, clat: 281, lat: 353, bw: 1183-1363-1403, c6%: 79.9 slat: 107, clat: 270, lat: 319, bw: 1192-1370-1406, c6%: 79.8 slat: 156, clat: 269, lat: 323, bw: 1187-1363-1398, c6%: 80.4 slat: 106, clat: 267, lat: 316, bw: 1183-1367-1402, c6%: 80.5 slat: 108, clat: 247, lat: 313, bw: 1186-1368-1404, c6%: 80.0 slat: 107, clat: 274, lat: 323, bw: 1188-1361-1399, c6%: 80.0 -Tero [1] https://lore.kernel.org/lkml/ZtHWkn2FJhAa+Vvo@fedora/T/ [2] https://lore.kernel.org/lkml/20241004101014.3716006-1-tero.kristo@xxxxxxxxxxxxxxx/
