Messages in this thread | | | Date | Fri, 27 Jan 2012 07:00:34 +0100 | From | Herbert Poetzl <> | Subject | Bad SSD performance with recent kernels |
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Dear Community!
Recently I decided to update the kernel on a Dell Laptop to a more recent version than 2.6.38.x, but experienced bad I/O performance with the new kernel, so I started to dig a little deeper and ended up with the following test:
1) download and extract kernel (on 2.6.38.8) 2) make defconfig 3) make localmodconfig 4) make 5) make modules_install install
Then I booted each kernel in single user and ran the following test script:
echo noop >/sys/class/block/sda/queue/scheduler for n in 1 2 3; do sync; echo $n > /proc/sys/vm/drop_caches; done /usr/bin/time -f "real = %e, user = %U, sys = %S, %P cpu" \ ionice -c0 nice -20 \ dd if=/dev/sda of=/dev/null bs=1M count=20480
echo deadline >/sys/class/block/sda/queue/scheduler for n in 1 2 3; do sync; echo $n > /proc/sys/vm/drop_caches; done /usr/bin/time -f "real = %e, user = %U, sys = %S, %P cpu" \ ionice -c0 nice -20 \ dd if=/dev/sda of=/dev/null bs=1M count=20480
echo cfq >/sys/class/block/sda/queue/scheduler for n in 1 2 3; do sync; echo $n > /proc/sys/vm/drop_caches; done /usr/bin/time -f "real = %e, user = %U, sys = %S, %P cpu" \ ionice -c0 nice -20 \ dd if=/dev/sda of=/dev/null bs=1M count=20480
note that the Laptop is a relatively modern Latitude E6400 with a Samsung 830 Series 256GB SSD
here are the surprising results:
@ linux 2.6.38.8 248 MB/s real = 86.74, user = 0.01, sys = 21.65, 24% cpu 248 MB/s real = 86.81, user = 0.02, sys = 21.75, 25% cpu 251 MB/s real = 85.63, user = 0.01, sys = 22.24, 25% cpu
@ linux 2.6.39.4 49.0 MB/s real = 438.79, user = 0.01, sys = 19.79, 4% cpu 25.7 MB/s real = 836.70, user = 0.02, sys = 18.39, 2% cpu 27.7 MB/s real = 776.53, user = 0.01, sys = 16.03, 2% cpu
@ linux 3.0.18 48.9 MB/s real = 439.07, user = 0.01, sys = 17.55, 4% cpu 25.0 MB/s real = 859.03, user = 0.01, sys = 16.97, 1% cpu 49.8 MB/s real = 431.61, user = 0.01, sys = 16.68, 3% cpu
@ linux 3.1.10 54.0 MB/s real = 398.23, user = 0.01, sys = 17.36, 4% cpu 29.4 MB/s real = 731.47, user = 0.01, sys = 17.14, 2% cpu 25.0 MB/s real = 859.35, user = 0.01, sys = 14.51, 1% cpu
@ linux 3.2.2 45.8 MB/s real = 468.85, user = 0.01, sys = 17.11, 3% cpu 44.8 MB/s real = 478.92, user = 0.01, sys = 17.02, 3% cpu 45.0 MB/s real = 476.91, user = 0.01, sys = 16.14, 3% cpu
I have no idea why the I/O performance is that bad on any kernel newer than 2.6.38.x, but I'm happy to test and/or try various configurations as time permits ...
The detailed test results as well as the dmesg and config of each kernel can be found here: http://vserver.13thfloor.at/Stuff/SSD
many thanks in advance, Herbert
here some technical information:
http://www.dell.com/us/dfb/p/latitude-e6400/pd SATA controller: Intel Corporation ICH9M/M-E SATA AHCI Controller (rev 03)
http://www.samsung.com/uk/consumer/memory-cards-hdd-odd/ssd/ssd/MZ-7PC256N/EU-spec Model=SAMSUNG SSD 830 Series, FwRev=CXM03B1Q supposed 520MB/s seq. read, 320MB/s seq. write, 75K IOPS
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