Messages in this thread | | | From | Rus <> | Date | Fri, 29 Apr 2016 16:36:16 +0300 | Subject | Fwd: Strange I/O slowdown with 4.x kernels |
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Hi,
After switching from 3.x to 4.x I'm observing strange filesystem (ext4 used) slowdown just after fresh boot - it is 100% reproducible. The simple test just after boot at root fs first shows the good performance :
dd if=/dev/zero of=/output bs=8k count=10k; rm -f /output 10240+0 records in 10240+0 records out 83886080 bytes (84 MB) copied, 0.5676 s, 150.3 MB/s
But after some small i/o stress (completed updatedb command for ex) the i/o speed drops dramatically :
dd if=/dev/zero of=/output bs=8k count=10k; rm -f /output 10240+0 records in 10240+0 records out 83886080 bytes (84 MB) copied, 19.5703 s, 4.3 MB/s
What is interesting is that hdparm test still shows normal performance :
hdparm -t /dev/sda1
/dev/sda1: Timing buffered disk reads: 448 MB in 3.01 seconds = 148.79 MB/sec
How to debug such thing (bissect can take too much time because of big version range) ? The config attached, this is ordinary 32-bit system with 32GB ECC RAM. The slowdown clearly triggered with last stable (4.5.2) and latest rc (4.6-rc5) kernels. The 3.x kernels do not have such bug. Can supply any additional info.
TIA, Rus
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