On Mon, Apr 19, 2021 at 7:57 PM Jens Axboe [off-list ref] wrote:

On 4/11/21 11:35 PM, Jinpu Wang wrote:

quoted

On Fri, Apr 9, 2021 at 11:03 PM Jens Axboe [off-list ref] wrote:

quoted

On 4/9/21 10:03 AM, Md Haris Iqbal wrote:

quoted

Hi Jens,

This version fixes the long lines in the code as per Christoph's comment.

I'd really like to see some solid justification for the addition,
though. I clicked the v1 link and it's got details on what you get out
of it, but not really the 'why' of reasoning for the feature. I mean,
you could feasibly have a blktrace based userspace solution. Just
wondering if that has been tried, I know that's what we do at Facebook
for example.

Hi Jens,

Thanks for the reply.
For the use case of the additional stats, as a cloud provider, we
often need to handle report from the customers regarding
performance problem in a period of time in the past, so it's not
feasible for us to run blktrace, customer workload could change from
time to time, with the additional stats, we gather through all metrics
using Prometheus, we can navigate to the period of time interested,
to check if the performance matches the SLA, it also helps us to find
the user IO pattern,  we can more easily reproduce.

My suggestion isn't to run just blktrace all the time, rather collect
the tracing info from there and store them away. Then you can go back
in time and see what is going on. Hence my questioning on adding this
new stat tracking, when it's already readily available to be consumed
by a small daemon that can continually track it in userspace.

--
Jens Axboe

Hi Jens,
The problem with using blktrace at production may cause a performance
drop ~30%. while with the block stats here, we only see ~3% when
enabled.
We did a benchmark with rnbd.

Fio config:
[global]
description=Emulation of Storage Server Access Pattern
bssplit=512/20:1k/16:2k/9:4k/12:8k/19:16k/10:32k/8:64k/4
fadvise_hint=0
rw=randrw:2
direct=1
random_distribution=zipf:1.2
#size=1G
time_based=1
runtime=10
ramp_time=1
ioengine=libaio
iodepth=128
iodepth_batch_submit=128
iodepth_batch_complete=128
numjobs=1
#gtod_reduce=1
group_reporting

[job1]
filename=/dev/rnbd0

blktrace command:
# blktrace -a read -a write -d /dev/rnbd0

read IOPS drops 35%, similar for write IOPS.

RNBD-No-blktrace  RNBD-With-blktrace

 102056.894311               -35.5%

The tests are done with v5.4.30.
Test hardware is
root@x4-left:~/haris/sds-perf# uname -a
Linux x4-left 5.10.30-pserver
#5.10.30-1+feature+linux+5.10.y+20210414.1233+e3dd267~deb10 SMP
x86_64 GNU/Linux
root@x4-left:~/haris/sds-perf# lscpu
Architecture:        x86_64
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
Address sizes:       46 bits physical, 48 bits virtual
CPU(s):              40
On-line CPU(s) list: 0-39
Thread(s) per core:  2
Core(s) per socket:  10
Socket(s):           2
NUMA node(s):        2
Vendor ID:           GenuineIntel
CPU family:          6
Model:               85
Model name:          Intel(R) Xeon(R) Silver 4114 CPU @ 2.20GHz
Stepping:            4
CPU MHz:             800.571
CPU max MHz:         3000.0000
CPU min MHz:         800.0000
BogoMIPS:            4400.00
Virtualization:      VT-x
L1d cache:           32K
L1i cache:           32K
L2 cache:            1024K
L3 cache:            14080K
NUMA node0 CPU(s):   0-9,20-29
NUMA node1 CPU(s):   10-19,30-39
Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr
pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe
syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts
rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq
dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm
pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes
xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3
cdp_l3 invpcid_single intel_ppin mba ibrs ibpb stibp tpr_shadow vnmi
flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 hle avx2 smep
bmi2 erms invpcid rtm cqm mpx rdt_a avx512f avx512dq rdseed adx smap
clflushopt clwb intel_pt avx512cd avx512bw avx512vl xsaveopt xsavec
xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local
dtherm ida arat pln pts pku ospke
root@x4-left:~/haris/sds-perf# ibstat
CA 'mlx5_0'
CA type: MT4115
Number of ports: 1
Firmware version: 12.26.4012
Hardware version: 0
Node GUID: 0xec0d9a0300c5fffc
System image GUID: 0xec0d9a0300c5fffc
Port 1:
State: Active
Physical state: LinkUp
Rate: 100
Base lid: 3
LMC: 0
SM lid: 3
Capability mask: 0x2651e84a
Port GUID: 0xec0d9a0300c5fffc
Link layer: InfiniBand
CA 'mlx5_1'
CA type: MT4115
Number of ports: 1
Firmware version: 12.26.4012
Hardware version: 0
Node GUID: 0xec0d9a0300c5fffd
System image GUID: 0xec0d9a0300c5fffc
Port 1:
State: Active
Physical state: LinkUp
Rate: 100
Base lid: 1
LMC: 0
SM lid: 1
Capability mask: 0x2651e84a
Port GUID: 0xec0d9a0300c5fffd
Link layer: InfiniBand

Thanks!