linux-ext4 - Re: High CPU Utilization When Copying to Ext4

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Date:	Wed, 29 Jun 2011 16:16:58 -0700
From:	Sean McCauliff <Sean.D.McCauliff@...a.gov>
To:	Andreas Dilger <adilger@...mcloud.com>
CC:	"Ted Ts'o" <tytso@....edu>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: High CPU Utilization When Copying to Ext4


On 06/28/2011 01:17 PM, Andreas Dilger wrote:

> Note that you need to be careful with FIEMAP for copying files...  There were
> some problems reported to this list with this, if the file was newly written.
> It is safest to always pass FIEMAP_FLAG_SYNC before copying the file to ensure
> the blocks are mapped to disk.

Thanks!

>
>> The copy has completed.  This is a snipped from top I had saved.  This machine has 4 cores and 8G of ram.  There are 32 threads doing copies.  At any time each has a directory to itself.
>>
>>     % cpu
>> 0573 root 20 0 7574m 1.9g 1356 S 204.3 24.9 3054:22 java
>> 27702 root 20 0 0 0 0 R 70.5 0.0 689:01.73 flush-253:2
>> 22467 root 20 0 0 0 0 S 22.6 0.0 7:55.98 kworker/3:1
>> 22351 root 20 0 0 0 0 S 21.6 0.0 9:42.58 kworker/1:3
>> 22686 root 20 0 0 0 0 S 21.3 0.0 0:26.19 kworker/2:0
>> 22679 root 20 0 0 0 0 S 13.8 0.0 0:29.14 kworker/0:1
>>    38 root 20 0 0 0 0 S 9.2 0.0 91:21.19 kswapd0
>> 22700 root 20 0 0 0 0 S 7.9 0.0 0:04.64 kworker/0:0
>> 10566 root 20 0 0 0 0 S 3.6 0.0 17:14.77 jbd2/dm-2-8
>>
>> If I remember correctly top said that: 97% of time was sys time.  So even the time used by Java was still almost all kernel time.    Only a few megabytes was actually swapped.
>
> Looking at the above, "java" is using by far the most memory/CPU, unless this
> program is not just doing the copy?

It does walk down the directory tree.  When it finds a directory it 
creates a new object in the thread work queue for the directory it 
found.  Threads read off the the queue creating directories in the 
destination and copying files to the destination.

>
> You could run oprofile to see where the CPU cycles are being used.
I will do this next time I'm running the copy.

Thanks,
Sean
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