fileio results

Random file I/O regressions on stock Linux kernels

Update: 05/05/2004: Andrew Morton posted on the linux-kernel mailing list the read-ahead patch against 2.6.6-rc3 that cuts the regression down to about 10% . The results of the patched 2.6.6-rc3 have been added to the results table below.

I ran the SysBench random file I/O test on stock 2.4 and 2.6 kernels and found significant regressions for 2.6 kernels that I failed to explain.

Test setup

The workloads were created by the SysBench fileio test with the following parameters:

Number of worker threads	16
Total file size	3 GB
Number of files	128
Test mode	random read/write
Read/write ratio	1.5
Block size	16 KB
Total number of requests	10000
fsync() frequency	100

The fileio test configured in this way creates 16 worker threads, each running random read/write I/O requests in blocks of 16 KB with a read/write ratio of 1.5. All I/O operations are evenly distributed among 128 files with a total file size of 3 GB. Each 100 requests, an fsync() operation is performed sequentially on each file. The total number of requests is limited by 10000.
The SysBench command line arguments for this configuration are the following:

sysbench --num-threads=16 --test=fileio --file-total-size=3G --file-test-mode=rndrw run

The filesystem used for the test runs was ext3 with data=ordered.

Hardware

The benchmarks hardware is an AMD Athlon 800 MHz with 640 MB RAM and an IBM IC35L040 IDE hard drive.

Kernel versions

I tested vanilla 2.4.25 (config), 2.6.5-bk2 (config) and 2.6.6-rc3 (config) (+ read-ahead patch) kernels with a default I/O scheduler for 2.4.25 kernel and anticipatory, deadline, CFQ and "noop" schedulers for 2.6.x kernels.

Results

The following table shows the results of the tests. Values represent the number of seconds required for the test to complete (lower is better).

	2.4.25	2.6.5-bk2	2.6.6-rc3	2.6.6-rc3 + patch
2.4.25 scheduler	77.5377
noop scheduler		165.3393	164.9486	94.0064
anticipatory scheduler		118.7450	125.1776	86.5459
deadline scheduler		130.3254	131.8903	92.8340
CFQ scheduler		146.4286	152.9280	95.7213