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SubjectRe: Linux 2.6.6 "IDE cache-flush at shutdown fixes"
Bartlomiej Zolnierkiewicz wrote:

> The other part of the story is a nasty bug in ide-disk.c driver:
>
> write_cache() is called with (drive->id->cfs_enable_2 & 0x300) as argument
> 'arg' of type 'int' and then this value is assigned to the 'drive->wcache'
> of type 'unsigned char' so drive->wcache == 0 because 0x3000 gets truncated.
>
> This bug has been present since introduction of drive->wcache (2.5.3),
> therefore we have never handled cache flush correctly before and never
> hit '& 0x2400' problem before.
>
> Linus & Alan, you were almost right after all, drive->wcache was almost
> always zero for normal disks before 2.6.6. It could be forced by user but
> only for disks having ATA-6 cache flush bits and was auto-set but only for
> removable disks (after Alan's fixes in 2.6.65). You lucky b*st*rds. ;-)
>
> Rene, that's why wcache is 0 in /proc/ide/hdX/settings for older kernels
> or with my 'bandaid' fixes for 2.6.6. 'hdparm -W1' should work but only on
> quite recent drives (having ATA-6 bits). However I don't know why you get
> regression in tiobench, we still need to explain this.

I'm afraid I can explain it. Even though hdparm -W0/-W1 didn't show up
in the settings, they certainly do take effect (on this drive). The bad
results I posted appear to have been with -W0. By default, and after
-W1, it's back up to normal again. Sorry if I confused the issue.

Rene.
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