Messages in this thread | | | Subject | Re: [PATCH] Add quick erase format option | From | Stefani Seibold <> | Date | Mon, 09 Aug 2010 15:37:07 +0200 |
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Am Montag, den 09.08.2010, 14:29 +0300 schrieb Artem Bityutskiy: > On Mon, 2010-08-09 at 10:52 +0200, Stefani Seibold wrote: > > Am Montag, den 09.08.2010, 09:37 +0100 schrieb David Woodhouse: > > > On Mon, 2010-08-09 at 09:25 +0100, stefani@seibold.net wrote: > > > > From: Stefani Seibold <stefani@seibold.net> > > > > > > > > This patch add a quick format option which skips erasing of already erased > > > > flash blocks. This is useful for first time production environments where > > > > the flash arrived erased. > > > > > > > > Signed-off-by: Stefani Seibold <stefani@seibold.net> > > > > > > This scares me, given the lengths we had to go to in JFFS2 to cope with > > > blocks which *look* like they're erased, but which actually start losing > > > data as soon as you start writing to them because the erase didn't > > > complete. > > > > > > > I know the drawback. This is why it is only an option which must be > > enabled. And in most use cases there is a subsequent ubimkvol, which > > will fail if the flash is not correct initialized. > > > > Flash are normally delivered erased. So this save in our production > > environment (Nokia Siemens Networks) about 5 minutes per device (256 MB > > NOR CFI Flash). > > > > The old JFFS2 was very fast to install the first time on a flash, it was > > only a simple mount of the MTD partition. > > Not sure what you do, but both UBI and UBIFS auto-format flash if it is > empty, and attaching empty flash should be very fast. >
I was never able to mount UBIFS without a previous ubimkvol, despite the flash is already erased.
> But yes, the first volume creation ioctl will block until everything is > erased, although this is just an implementation issue and in theory, > fixable. >
Here are my timing results for mounting an empty flash as UBIFS:
ubiattach /dev/ubi_ctrl -m 5 -d 1 --> 2.023 sec ubimkvol /dev/ubi1 -m -N flash --> 294.574 sec mount -t ubifs -o sync ubi1:flash /mnt --> 0.221 sec
or
ubiformat /dev/mtd5 --> 299.111 sec ubiattach /dev/ubi_ctrl -m 5 -d 1 --> 0.129 sec ubimkvol /dev/ubi1 -m -N flash --> 1.784 sec mount -t ubifs -o sync ubi1:flash /mnt --> 0.220 sec
So there is no real benefit between an empty flash and a formated flash.
And this are the timing results for formating and mounting an empty flash with my patched ubiformat tool:
ubiformat /dev/mtd5 -E --> 5.475 sec ubiattach /dev/ubi_ctrl -m 5 -d 1 --> 0.130 sec ubimkvol /dev/ubi1 -m -N flash --> 1.699 sec mount -t ubifs -o sync ubi1:flash /mnt --> 0.220 sec
As you can see this is 296,818 vs. 7,522 or 40 times faster!
But maybe i do something wrong. Could you explain this?
> > Which the quick format option i have now only a slightly first time > > installation overhead compared to JFFS2. Without this option the > > overhead is more than 5 minutes. > > Are you flashing an UBI image in production? Then what you can do if you > want to be faster is to flash only the blocks which contain image date, > and leave the rest intact, UBI will erase them and write EC header to > them when you first boot the device. >
No, we only initialize the flash, mount the UBIFS it and copy files.
> So I think it is better to add an --pristine-flash option, or something > like this. In this case ubiformat won't erase anything, and will assume > everything is 0xFFed without reading. This should be faster and I think > is better to do. >
My patch assumes nothing, it check if the EC header is 0xff and i think this is safer than your suggestion. My patch skips the erase if all bytes in the header are 0xff skip, otherwise erase it.
- Stefani
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