writing to jffs2 is so slow?

writing to jffs2 is so slow?

[Xiaogeng (Shawn) Jin]

Hi,

I have an empty mtd partition (capacity is 16 MB) where a jffs2 fs is 
mounted. The strange observation is that making a first directory on 
that partition takes almost 2 minutes. So far I observed this behaviour 
just when making the first directory and just on that particular 
partition. Can anyone help me to explain this? Is there anything wrong 
with flash memory (hardware) or MTD device driver or JFFS2? Thanks.

- Shawn.

RE: writing to jffs2 is so slow?

[Thomas TESTASECCA]

Hi Shawn,

All i can say is that it's not normal !! :)
Try to turn off the debugging mode for mtd & jffs2 (into "make menuconfig").
good luck
tom

-----Message d'origine-----
De : linux-mtd-admin@lists.infradead.org
[mailto:linux-mtd-admin@lists.infradead.org]De la part de Xiaogeng
(Shawn) Jin
Envoye : jeudi 5 septembre 2002 23:10
A : linux-mtd@lists.infradead.org
Objet : writing to jffs2 is so slow?


Hi,

I have an empty mtd partition (capacity is 16 MB) where a jffs2 fs is
mounted. The strange observation is that making a first directory on
that partition takes almost 2 minutes. So far I observed this behaviour
just when making the first directory and just on that particular
partition. Can anyone help me to explain this? Is there anything wrong
with flash memory (hardware) or MTD device driver or JFFS2? Thanks.

- Shawn.


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: writing to jffs2 is so slow?

[Kenneth Johansson]

On Thu, 2002-09-05 at 23:09, Xiaogeng (Shawn) Jin wrote:
> Hi,
> 
> I have an empty mtd partition (capacity is 16 MB) where a jffs2 fs is 
> mounted. The strange observation is that making a first directory on 
> that partition takes almost 2 minutes. So far I observed this behaviour 
> just when making the first directory and just on that particular 
> partition. Can anyone help me to explain this? Is there anything wrong 
> with flash memory (hardware) or MTD device driver or JFFS2? Thanks.
> 

The thing is that jffs2 seems to mark the whole disk dirty and has to re
erase the whole disk before you can store anything on it. This happens
only the first time. If you wait a few minutes after you do the mount
you should see no delay in creating directories and files.

Maybe it's possible to do a format command that creates a disk that is
empty and prevents the jffs2 code to reformat every block.


-- 
Kenneth Johansson	
Ericsson AB                       Tel: +46 8 404 71 83
Borgafjordsgatan 9                Fax: +46 8 404 72 72
164 80 Stockholm                  kenneth.johansson@etx.ericsson.se

Re: writing to jffs2 is so slow?

[Xiaogeng (Shawn) Jin]

> Maybe it's possible to do a format command that creates a disk that is
> empty and prevents the jffs2 code to reformat every block.

A format command? What command formats MTD devices (my flash is NOR)? 
Thanks.

- Shawn.

Re: writing to jffs2 is so slow?

[Jörn Engel]

On Fri, 6 September 2002 10:14:24 -0700, Xiaogeng (Shawn) Jin wrote:
> >Maybe it's possible to do a format command that creates a disk that is
> >empty and prevents the jffs2 code to reformat every block.
> 
> A format command? What command formats MTD devices (my flash is NOR)? 
> Thanks.

Try eraseall from the utils.
With that, jffs2 just writes the erase markers to flash, 12 bytes per
erase block.

Jörn

-- 
Beware of bugs in the above code; I have only proved it correct, but
not tried it.
-- Donald Knuth

Re: writing to jffs2 is so slow?

[Xiaogeng (Shawn) Jin]

>>>Maybe it's possible to do a format command that creates a disk that is
>>>empty and prevents the jffs2 code to reformat every block.
>>
>>A format command? What command formats MTD devices (my flash is NOR)? 
>>Thanks.
> 
> Try eraseall from the utils.
> With that, jffs2 just writes the erase markers to flash, 12 bytes per
> erase block.

Well, that's just what I did. Then making a first directory takes 2 minutes.

- Shawn.

Re: writing to jffs2 is so slow?

[David Woodhouse]

xjin@redswitch.com said:
> > Try eraseall from the utils.
> > With that, jffs2 just writes the erase markers to flash, 12 bytes per
> > erase block.

No, JFFS2 cannot trust that 'empty' blocks really have been properly 
erased, and must erase them again, writing a 'cleanmarker' node to them 
when the erase is complete.

> Well, that's just what I did. Then making a first directory takes 2
> minutes. 

JFFS2 is busy erasing every block on the file system. You have to wait 
until it's done before you can write.

Hacking the 'eraseall' program so it writes a 'cleanmarker' node to the 
beginning of every block erased is left as an exercise for the reader.

Other possibilities include a mount time option to tell JFFS2 that it 
should trust the flash and not re-erase the blocks, and/or changing the 
jffs2_write_super()/jffs2_erase_pending_blocks() to only erase a few blocks 
at a time, so you only have to wait for a few blocks to be erased, not the 
whole flash.


--
dwmw2

Re: writing to jffs2 is so slow?

[Jörn Engel]

On Fri, 6 September 2002 11:32:01 -0700, Xiaogeng (Shawn) Jin wrote:
> >
> >Try eraseall from the utils.
> >With that, jffs2 just writes the erase markers to flash, 12 bytes per
> >erase block.
> 
> Well, that's just what I did. Then making a first directory takes 2 minutes.

Yes, you are right, silly me.

Without the erase markers, jffs2 does not trust those blocks. They
could have been deleted almost completely before a power fail. And
that little almost will cause random bit changes sometime liter, which
is bad.

You could maybe use mkfs.jffs2 with the -p option. Might work, but I
cannot check it right now.

Alternatively, you could hack the eraseall code, looking at mkfs.jffs2
for references, to write the erase markers into the flash.

Yet another alternative, you could write the erase markers via the
mtdblock device. Write one into a file, pad to erase block size,
append said file multiple times to itself and write it to flash.

Jörn

-- 
Victory in war is not repetitious.
-- Sun Tzu

Re: writing to jffs2 is so slow?

[Joakim Tjernlund]

----- Original Message -----
From: "David Woodhouse" <dwmw2@infradead.org>
To: "Xiaogeng (Shawn) Jin" <xjin@redswitch.com>
Cc: "Jörn Engel" <joern@wohnheim.fh-wedel.de>; "Kenneth Johansson" <kenneth.johansson@etx.ericsson.se>; "Mtd"
<linux-mtd@lists.infradead.org>
Sent: den 6 september 2002 20:54
Subject: Re: writing to jffs2 is so slow?


>
> xjin@redswitch.com said:
> > > Try eraseall from the utils.
> > > With that, jffs2 just writes the erase markers to flash, 12 bytes per
> > > erase block.
>
> No, JFFS2 cannot trust that 'empty' blocks really have been properly
> erased, and must erase them again, writing a 'cleanmarker' node to them
> when the erase is complete.
>
> > Well, that's just what I did. Then making a first directory takes 2
> > minutes.
>
> JFFS2 is busy erasing every block on the file system. You have to wait
> until it's done before you can write.

I think that can be fixed(or at least better). Instead of eraseing all blocks first and
then write cleanmarker to those blocks, make it erase one block and write
cleanmarker erase the next block and write it's cleanmarker and so on.

That way you will free up erase blocks as they become ready and you don't have to watch
the use % in df slowly raise to 100% and the suddenly drop to the real usage.

   Jocke

Re: writing to jffs2 is so slow?

[David Woodhouse]

Joakim.Tjernlund@lumentis.se said:
>  I think that can be fixed(or at least better). Instead of eraseing
> all blocks first and then write cleanmarker to those blocks, make it
> erase one block and write cleanmarker erase the next block and write
> it's cleanmarker and so on.

> That way you will free up erase blocks as they become ready and you
> don't have to watch the use % in df slowly raise to 100% and the
> suddenly drop to the real usage.

Agreed.

--
dwmw2