Messages in this thread | | | Subject | huge improvement with per-device dirty throttling | From | "Jeffrey W. Baker" <> | Date | Tue, 21 Aug 2007 23:37:18 -0700 |
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I tested 2.6.23-rc2-mm + Peter's per-BDI v9 patches, versus 2.6.20 as shipped in Ubuntu 7.04. I realize there is a large delta between these two kernels.
I load the system with du -hs /bigtree, where bigtree has millions of files, and dd if=/dev/zero of=bigfile bs=1048576. I test how long it takes to ls /*, how long it takes to launch gnome-terminal, and how long it takes to launch firefox.
2.6.23-rc2-mm-bdi is better than 2.6.20 by a factor between 50x and 100x.
1.
sleep 60 && time ls -l /var /home /usr /lib /etc /boot /root /tmp
2.6.20: 53s, 57s 2.6.23: .652s, .870s, .819s
improvement: ~70x
2.
sleep 60 && time gnome-terminal
2.6.20: 1m50s, 1m50s 2.6.23: 3s, 2s, 2s
improvement: ~40x
3.
sleep 60 && time firefox
2.6.20: >30m 2.6.23: 30s, 32s, 37s
improvement: +inf
Yes, you read that correctly. In the presence of a sustained writer and a competing reader, it takes more than 30 minutes to start firefox.
4.
du -hs /bigtree
Under 2.6.20, lstat64 has a mean latency of 75ms in the presence of a sustained writer. Under 2.6.23-rc2-mm+bdi, the mean latency of lstat64 is only 5ms (15x improvement). The worst case latency I observed was more than 2.9 seconds for a single lstat64 call.
Here's the stem plot of lstat64 latency under 2.6.20
The decimal point is 1 digit(s) to the left of the |
0 | 00000000000000000000000000000000000000000000000000000000000000000000+1737 2 | 177891223344556788899999 4 | 00000111122333333444444555555556666666666667777777777777788888888888+69 6 | 00000111222334557778999344677788899 8 | 0123484589 10 | 020045 12 | 1448239 14 | 1 16 | 5 18 | 399 20 | 32 22 | 80 24 | 26 | 2 28 | 1
Here's the same plot for 2.6.23-rc2-mm+bdi. Note the scale
The decimal point is 1 digit(s) to the left of the |
0 | 00000000000000000000000000000000000000000000000000000000000000000000+2243 1 | 1222255677788999999 2 | 0011122257 3 | 237 4 | 3 5 | 6 | 7 | 3 8 | 45 9 | 10 | 11 | 12 | 13 | 9
In other words, under 2.6.20, only writing processes make progress. Readers never make progress.
5.
dd writeout speed
2.6.20: 36.3MB/s, 35.3MB/s, 33.9MB/s 2.6.23: 20.9MB/s, 22.2MB/s
2.6.23 is slower when writing out, because other processes make progress
My system is a Core 2 Duo, 2GB, single SATA disk.
-jwb
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