Zen kernel improvements

CPU

• Tweaked CFS scheduler for lower latency. 7de2596b35ac1dbf55fb384f3d668a7315635c0b

  • Scheduling latency: 6 -> 4 ms
  • Minimal granularity: 0.75 -> 0.4 ms
  • Wakeup granularity: 1 -> 0.5 ms
  • CPU migration cost: 0.5 -> 0.25 ms
  • Bandwidth slice size: 5 -> 3 ms
  • Number of threads running: 8 -> 10

• Forced interrupt request threading by default. e9a38f81725b3024defed48f6f3efbbd622c2746

• Tweaked on-demand scheduler. 070b844e9e5485b8c14c85ae48747157893df148

  • Samping down factor: 1 -> 5

MuQSS

MuQSS is not enabled by default. Can be enabled with CONFIG_SCHED_MUQSS variable.

• Disable yielding as it caused performance issues. ac994d428ce6eaa4c05a2b4a2083a32fcc55c682

• Reduced the cpu percentage that isochronous processes (SCHED_ISO) can use. ec2c919523eb93f34178b8df17d3351990d31907

  • Isochronous processes allowed time: 70% -> 25%

• Round robin time reduced. 07224ba0c5d52ac05a08c28705f2578468e7a5be

  • Round robin interval: 6 ms -> 2 ms

• Tweaked on-demand scheduler. 070b844e9e5485b8c14c85ae48747157893df148

  • Samping down factor: 1 -> 5
  • Frequency up threshold: 95 -> 45
  • Micro frequency up threshold: 80 -> 40

• MuQSS tweeks documentation updated. add8f00727055356b90337313a23a3992e547d8d

RAM

• LZ4 compression algorithm for zswap instead of LZO. 90f3ec26286144951705914bec821254ce9e4b11

• zswap enabled by default. 7444df2ac4e2c4b47cfc5c6b1b64f54eb09e3800

• z3fold is now default compression allocator with stronger compression. 4eab5c9ea4fd3e6595b664a429869f4611fad7d4

• Transparent Huge Page defragmentation strategy to defer+madvise. 11c4c38b31dce0ff44972f495da537b3fbb0945f

• Unevictable memory not allowed to be compacted. 394ae0c10f1a73cc0b9a738e5e4c070076cc7727

• Writeback triggers at higher memory threshold. 598f06b26605fd12c5d955ef86ff3add25343efc

  • Background writeback threshold: 10% -> 20%
  • Sync writeback threshold: 20% -> 50%

IO

• BFQ (budget fair queueing) as default scheduler for multiqueue block devices. 07b36ce250f292fc4590cbadb4c5797c54f528b5

• Increase block layer queue depth to 512. 9646e76dda2341d1cdd3796690a1f1861ebcb1bd

  • Reverted. 99a750246b733bf1f9178458c5b8193ad4626de0

Drivers

• Virtual (SCSI) Host Bus Adapter (VHBA) driver added. Allows to emulate CD/DVD devices. ae2bd58fe11e9963d350cfd031da934231435e24

Misc

• Allowed O3 level of optimizations outside of ARC architecture. 8e4c45742cfca87c0cc44e7969ab8826be9139be

• Added ZEN_INTERACTIVE compile variable that enables the latency improvements. 827501ad72d510cb15ca96495b2233606b739f5e