[RFC PATCH 0/2] introduce precised blk-throttle control

[zhaoyang.huang]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

There is always an error between blk-throttle's configuration and the
real value which should be introduced by over-sized bio as there is no
control on ra->size during readahead. This series patches would like to
introduce the helper function to provide the bytes budgt and apply it
on readahead.

Please find below for the fio test result on v6.6 which presents 2%-10%
improvement for BW and lat. Besides, we can also observed stable BW
instantaneous and lower stdev value during the test.

blkio.throttle.read_bps_device = 1MB/s
   before:  read: IOPS=223, BW=894KiB/s (915kB/s)(175MiB/200919msec)
   after :  read: IOPS=239, BW=960KiB/s (983kB/s)(153MiB/163105msec)

   before:  clat (usec): min=4, max=16795k, avg=4468.74, stdev=265746.14
   after :  clat (usec): min=11, max=209193, avg=4105.22, stdev=27188.04

   before:  lat  (usec): min=6, max=16795k, avg=4470.57, stdev=265746.14
   after :  lat  (usec): min=16, max=209197, avg=4120.03, stdev=27188.04


blkio.throttle.read_bps_device = 10MB/s
   before:  read: IOPS=2380, BW=9524KiB/s (9752kB/s)(1007MiB/108311msec)
   after :  read: IOPS=2438, BW=9754KiB/s (9989kB/s)(1680MiB/176405msec)

   before:  clat (usec): min=4, max=2494.6k, avg=412.72, stdev=25783.51
   after :  clat (usec): min=4, max=201817, avg=399.58, stdev=8268.85

   before:  lat  (usec): min=6, max=2494.6k, avg=414.48, stdev=25783.51
   after :  lat  (usec): min=6, max=201819, avg=402.10, stdev=8268.85

blkio.throttle.read_bps_device = 20MB/s
fio ... -numjobs=8 ...

    before : IOPS=37.9k, BW=148MiB/s (155MB/s)(11.6GiB/80333msec)
    after  : IOPS=39.0k, BW=153MiB/s (160MB/s)(15.6GiB/104914msec)

    before : clat (usec): min=4, max=1056.6k, avg=197.23, stdev=10080.69
    after  : clat (usec): min=4, max=193481, avg=188.83, stdev=4651.29

    before : lat (usec): min=5, max=1056.6k, avg=200.48, stdev=10080.76
    after  : lat (usec): min=5, max=193483, avg=192.68, stdev=4651.87

blkio.throttle.read_bps_device = 30MB/s
fio ... -numjobs=8 ...

    before : IOPS=57.2k, BW=224MiB/s (234MB/s)(15.6GiB/71561msec)
    after  : IOPS=58.5k, BW=229MiB/s (240MB/s)(15.6GiB/69996msec)

    before : clat (usec): min=4, max=1105.5k, avg=126.20, stdev=6419.22
    after  : clat (usec): min=4, max=183956, avg=120.60, stdev=2957.28

    before : lat (usec): min=5, max=1105.5k, avg=129.45, stdev=6419.29
    after  : lat (usec): min=5, max=183958, avg=124.40, stdev=2958.18

Zhaoyang Huang (2):
  block: introduce helper function to calculate bps budgt
  mm: introduce budgt control in readahead

 block/blk-throttle.c       | 44 ++++++++++++++++++++++++++++++++++++++
 include/linux/blk-cgroup.h | 10 +++++++++
 mm/readahead.c             | 33 ++++++++++++++++++++--------
 3 files changed, 78 insertions(+), 9 deletions(-)

-- 
2.25.1