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Date:	Wed, 19 Mar 2014 09:35:03 +0000
From:	bugzilla-daemon@...zilla.kernel.org
To:	linux-ext4@...r.kernel.org
Subject: [Bug 71641] Unreasonable performance degradation in ext4 with full
 data journaling

https://bugzilla.kernel.org/show_bug.cgi?id=71641

--- Comment #3 from Chia-Hung Chang <fredchang.tc@...il.com> ---
Test command :  dd if=/dev/zero of=/share/CACHEDEV2_DATA/orderno5G bs=1M
count=5120

The results of block trace can be download as follow.
https://dl.dropboxusercontent.com/u/32959539/blktrace_original_data.7z

The results of btt can be download as follow.
https://dl.dropboxusercontent.com/u/32959539/blktrace_output.7z

There are three folders:
/journal              -->ext4,data=journal              with 375MB/s
/order_delalloc       -->ext4,data=ordered,delalloc     with 937MB/s
/order_nodelalloc     -->ext4,data=ordered,nodelalloc   with 353MB/s


The size of write request with data=ordered,delalloc is 64k mostly.
The size of write requests with data=journal and data=ordered,nodelalloc are 4k
mostly. 

If we observe the average Q2Q in btt results, which means time interval between
requests, we have

/journal           0.00081
/order_nodelalloc  0.00031

It seems to be the reason of performance degradation.
Is any one know why the time interval of requests is significantly longer with
data=journal?

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