Messages in this thread | | | From | "Mudama, Eric" <> | Subject | RE: [PATCH] ide write barrier support | Date | Fri, 17 Oct 2003 10:07:09 -0600 |
| |
> -----Original Message----- > From: Jens Axboe [mailto:axboe@suse.de] > > Yes that would be very nice, but unfortunately I think FUA in ATA got > defined as not implying ordering (the FUA write would typically go > straight to disk, ahead of any in-cache dirty data). Which > makes it less > useful, imo.
None of the TCQ/FUA components of the spec mention ordering. According to the "letter" of the specification, if you issue two queued writes for the same LBA, the drive has the choice of which one to do first and which one to put on the media first, which is totally broken in common sense land.
Luckilly, us drive guys are a bit smarter (if only a bit)...
If you issue a FUA write for data already in cache, and you put the FUA write onto the media, there's no problem if you discard the cached data that you were going to write.
In drives with a unified cache, they'll always be consistent provided the overlapping interface transfers happen in the same order they were issued.... this is common sense.
However, you're right in that non-overlapping cached write data may stay in cache a long time, which potentially gives you a very large time hole in which your FUA'd data is on the media and your user data is still hangin' in the breeze prior to a flush on a very busy drive. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |