Hello,
These patches intruduce a mechanism for limiting device frequencies via
PM QoS when latency-sensitive threads block on IO. Stroage device (like
UFS) use the "devfreq_monitor" mechanism to automatically scale
frequency based on IO workloads. However, the hysteresis in IO workload
detection, it will lead IO request to be processed at low frequency.
Original devfreq_monitir frequency scaling timeline:
|--- latency-intensive process working ------------
|****+**+**|***+++*++*|*++++++++*|**+++++***|*++++++++*|
| |- high load and scale up frequency
|-------- low frequency ----|-- high frequency ---|
([+] have IO request [*] nothing to do)
Now, the patches provided here intruduce a mechanism for the block layer
to add constraints to device frequecny through PM QoS framework, with
configurable sysfs knobs per block device. Doing following config in my
test system:
/sys/block/sda/dev_freq_timeout_ms = 30
This constraints is removed if there is no block IO for 30ms.
Enhanced frequency scaling timeline:
|--- latency-intensive process working ------------
|****+**+**|***+++*++*|*++++++++*|**+++++***|*++++++++*|
|- add device frequecy PM QoS constraints----------
|- scale up frequency
|-low-|------------ high frequency ---------------|
Here are my example system detail:
- SoC: Qualcomm Snapdragon (1+3+4 core cluster)
- Stroage: UFS 4.1
- Fio Version: 3.9
- Global fio config:
--rw=randread --bs=64k --iodepth=1 \
--numjobs=5 --time_based --runtime=10 \
--ioengine=libaio --hipri --cpus_allowed=3
(job1~5 startdelay = [0s, 20s, 40s, 60s, 80s])
- Local fio config:
-Test case 1:
--rate=10ms
-Test case 2:
--rate=0ms
Runing the same fio test used above with enhanced frequency scaling
enabled/disabled, I get:
Test case 1:
enabled: clat (usec): min=141, max=872, avg=550
disabled: clat (usec): min=210, max=899, avg=635
Test case 2:
enabled: BW=388.6(MB/s)
disabled: BW=378.2(MB/s)
So the intermittent workloads test(case 1) show >10% latency
improvement. The continuous workloads test(case2) show about 5%
bandwidth improvement.This mechanism delivers greater performance gains
under intermittent workloads compared to continuous workloads scenarios.
Any thoughts about the patches and the approach taken?
Wang Jianzheng (3):
block/genhd: add sysfs knobs for the device frequency PM QoS
block: add support for device frequency PM QoS tuning
scsi: ufs: core: Add support for frequency PM QoS tuning
block/blk-mq.c | 58 +++++++++++++++++++++++++++++++++++++++
block/genhd.c | 23 ++++++++++++++++
drivers/ufs/core/ufshcd.c | 44 +++++++++++++++++++++++++++++
include/linux/blkdev.h | 11 ++++++++
include/linux/pm_qos.h | 6 ++++
5 files changed, 142 insertions(+)
--
2.34.1
