On 21/06/10 21.14, Christoph Hellwig wrote: > On Mon, Jun 21, 2010 at 08:56:55PM +0200, Jens Axboe wrote: >> FWIW, Windows marks meta data writes and they go out with FUA set >> on SATA disks. And SATA firmware prioritizes FUA writes, it's essentially >> a priority bit as well as a platter access bit. So at least we have some >> one else using a meta data boost. I agree that it would be a lot more >> trivial to add the annotations if they didn't have scheduler impact >> as well, but I still think it's a sane thing. > > And we still disable the FUA bit in libata unless people set a > non-standard module option.. Yes, but that's a separate thing. The point is that boosting meta data IO is done by others as well. That we don't fully do the same on the hw side is a different story. That doesn't mean that the io scheduler boost isn't useful. >>>> Reads are sync by nature in the block layer, so they don't get that >>>> special annotation. >>> >>> Well, we do give them this special annotation in a few places, but we >>> don't actually use it. >> >> For unplugging? > > We use the explicit unplugging, yes - but READ_META also includes > REQ_SYNC which is not used anywhere. That does look superfluous. >>> But that leaves the question why disabling the idling logical for >>> data integrity ->writepage is fine? This gets called from ->fsync >>> or O_SYNC writes and will have the same impact as O_DIRECT writes. >> >> We have never enabled idling for those. O_SYNC should get a nice >> boost too, it just needs to be benchmarked and tested and then >> there would be no reason not to add it. > > We've only started using any kind of sync tag last year in ->writepage in > commit a64c8610bd3b753c6aff58f51c04cdf0ae478c18 "block_write_full_page: > Use synchronous writes for WBC_SYNC_ALL writebacks", switching from > WRITE_SYNC to WRITE_SYNC_PLUG a bit later in commit > 6e34eeddf7deec1444bbddab533f03f520d8458c "block_write_full_page: switch > synchronous writes to use WRITE_SYNC_PLUG" > > Before that we used plain WRITE, which had the normal idling logic. Plain write does not idle. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
