Re: JFFS2 access time

[DMcLeod <dmcleod@bittware.com>]

Josh Boyer wrote:
> On Wed, 16 Jan 2008 08:57:50 -0500
> DMcLeod <dmcleod@bittware.com> wrote:
>
>   
>> Hi all,
>>
>> We are using uClinux git 2.6.23. We have 4 2.5MB files sitting in a 
>> directory on a ~40MB jffs2 partition (on NOR flash). The very first time 
>> we do an 'ls' in that directory, the response takes literally minutes. 
>> After the initial delay, any accesses to those files are very 
>> quick.,,
>>     
>
> That is normal for large files.  JFFS2 has do the CRC checking on all
> the nodes for those large files.  That is a lot of nodes to check.  You
> might want to look into using the eraseblock summary feature.
>
>   
>> Originally, we started off with the Microtronix 1.4 kernel and 
>> it did not have this problem. The pre-git version of uClinux-dist had 
>> this problem but not as severe - it was more like 40 seconds to list the 
>> contents of that directory.
>>     
> I have no idea what those two kernels are, but older JFFS2 used to do
> all the CRC checking at mount time.  So mount would be slow and runtime
> access would be relatively quick.
>   
The Microtronix kernel is the kernel built by Altera's Quartus 6.1 
suite. By "pre-git" version, we just meant the packaged version from 
nioswiki, rather than getting it from the git server.

At any rate, it turns out that having the verbosity level set to 2 in 
the jffs2 section of menuconfig was our problem. The kernel was so 
dragged down by having to bombard /proc/kmsg with jffs2 printk's that it 
caused the huge delays we were seeing. We set verbosity back to 0 and 
all is well.

Thanks :-)
> josh
>
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