On 3/6/08 9:30 AM, Grant Erickson wrote:
I am continuing some experiments in booting Linux w/ a flattened device tree via u-boot (1.3.2-rc3) from JFFS2 on NAND on an AMCC "Haleakala" board and am curious if anyone has come up with some quantitative performance characterizations of the various options (in all cases, u-boot lives on NOR flash). The options I am evaluating are:
- Put uImage and haleakala.dtb in their own "raw" NAND slices and boot with u-boot nand commands:
[ ... details omitted ... ]
Qualitative performance: Nearly instantaneous.
As expected, in this case the qualitative, subjective time to seeing "Linux version 2.6.25-rc3-00951-g6514352-dirty ..." is nearly instantaneous.
- Put uImage and haleakala.dtb as files in /boot in the ~12 MB JFFS2 root file system image in the ~60 MB "root" NAND slice and boot with u-boot fsload commands:
[ ... details omitted ... ]
2a) With CFG_JFFS2_SORT_FRAGMENTS enabled.
Qualitative performance: Takes the better part of 30-35 minutes.
As expected with the in-documentation warnings about CFG_JFFS2_SORT_FRAGMENTS and looking at the code in u-boot/fs/jffs2/jffs2_nand_1pass.c, the qualitative, subjective time to seeing the Linux version banner is slow, slow and slow.
2b) With CFG_JFFS2_SORT_FRAGMENTS disabled.
Qualitative performance: Takes about 30 seconds to two minutes.
- This is a hybrid approach that I am setting up right now and is where I am
curious if anyone has done plots of fsload time on JFFS2 + NAND relative to file system size.
Here, we use a separate 4 MB "/boot" JFFS2 file system for uImage and haleakala.dtb files and a 60 MB "/" JFFS2 file system for the root file system.
[ ... details omitted ... ]
3a) With CFG_JFFS2_SORT_FRAGMENTS enabled.
Shouldn't be necessary since the /boot file system would only ever be accessed read-only and updated by nandwrite, not individual file updates.
3b) With CFG_JFFS2_SORT_FRAGMENTS disabled.
Qualitative performance: TBD <= 2b
For what it's worth, the results of (3b) above with a 4 MB "boot" JFFS2 file system were the same as (2b) where "/boot" was just a subdirectory of the 12 MB (62 MB total NAND space) "/" JFFS2 file system:
In short, qualitative performance: Takes about 30 seconds to two minutes.
So, with CFG_JFFS2_SORT_FRAGMENTS disabled it would appear that fsload on JFFS2 is O(1) with respect to one or all of: file system size, inodes or dirents in the 4 MB to 64 MB range.
Regards,
Grant