lkml.org 
[lkml]   [2012]   [Jan]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectBad SSD performance with recent kernels

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







\
 
 \ /
  Last update: 2012-01-27 07:31    [from the cache]
©2003-2011 Jasper Spaans