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Message #30160
[Bug 1242812] Re: ext4 random block I/O write performance regression with 3.11 Saucy Kernel
** Branch linked: lp:ubuntu/saucy-proposed/linux-exynos5
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https://bugs.launchpad.net/bugs/1242812
Title:
ext4 random block I/O write performance regression with 3.11 Saucy
Kernel
Status in “linux” package in Ubuntu:
Fix Committed
Bug description:
Commit e7ea81db5(ext4: restructure writeback path) introduced a
performance regression with random writes. Using tools such as
bonnie++, writes with dd or even stress testing with tools such as
'stress' one can observe a 10%-20% performance regression.
SRU Justification:
Commit e7ea81db5(ext4: restructure writeback path) introduced a
performance regression with random writes. Using tools such as
bonnie++, writes with dd or even stress testing with tools such as
'stress' one can observe a 10%-20% performance regression.
Impact:
Write performance is diminished causing a noticeable regression
compared to previous released kernels.
Fix:
Two patches are required:
a) upstream fix 9c12a83 which fixes the overly aggressive writing back of pages which ultimulately resulted in more seeking and
less performance.
b) commit aeac589a7 from the dev branch of kernel/git/tytso/ext4.git
which ensures no more pages than nr_to_write can be added to the
extent for mapping.
Testcase:
Using stress-ng on a 2 CPU machine run:
stress-ng --hdd 2 --hdd-ops 200000
(see: git://kernel.ubuntu.com/cking/stress-ng.git)
With the fix, this consistently runs ~10-20% faster than the non-fixed
kernel.
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References