Messages in this thread |  | | Date | Mon, 24 Sep 2001 18:40:08 +0200 | From | < ( Marc) (A.) (Lehmann )> | Subject | Re: [reiserfs-list] Re: [PATCH] 2.4.10 improved reiserfs a lot, but could still be better |
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On Mon, Sep 24, 2001 at 09:15:19AM -0700, Nicholas Knight <tegeran@home.com> wrote: [turning off write-cache] > I'm sorry, but that's not acceptable.
(I had it turned off for a long time, until I reasoned: real power-outages are very rare, so I can leave it turned on anyways and risk a filesystemcheck after outages).
The reason this kills performance ALWAYS is that ide does not support large enough transfer sizes (8-32k on most drives) to fill one track.
Turning off write caching has a big chance of lowering your transaction throughput to the drive's RPM. Combined with linux' not-that-optimal elevator and write behaviour this has good chances of costing a lot of performance.
TCQ will obviously help, but I somehow doubt it will work fine - even with SCSI TCQ is a nightmare (the aic7xxx drive regularly kills my system if tagged queueing is enabled for example). IDE currently is a mess (I do _not_ expect my drive performance to simply halve just because two devices to share the bus, even if this is how conservative ide is destined to work).
I am convinced that there is a way of creating a hard write barrier (e.g. a cache flush that waits) with most if not all ide disks - putting them into powersave should work, if nothing else ;)
So apart from driver issues (such as TCQ), the mid-layer needs to be improved (and plans already exist) to support semi-ordered writes and give as much control over the device cache as possible.
Not to mention that the VM needs improvements here as well.
I didn't say much more than Alan implied: we have to live with it, so we better think about making it work.
-- -----==- | ----==-- _ | ---==---(_)__ __ ____ __ Marc Lehmann +-- --==---/ / _ \/ // /\ \/ / pcg@goof.com |e| -=====/_/_//_/\_,_/ /_/\_\ XX11-RIPE --+ The choice of a GNU generation | | - 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/
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