Messages in this thread | | | Date | Mon, 4 Mar 2002 19:57:23 +0000 | From | "Stephen C. Tweedie" <> | Subject | Re: [PATCH] 2.4.x write barriers (updated for ext3) |
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Hi,
On Mon, Mar 04, 2002 at 08:48:02PM +0100, Daniel Phillips wrote: > On March 4, 2002 07:05 pm, Stephen C. Tweedie wrote: > > Also, as soon as we have journals on external devices, this whole > > thing changes entirely. We still have to enforce the commit ordering > > in the journal, but we also still need the ordering between that > > commit and any subsequent writeback, and that obviousy can no longer > > be achieved via ordered tags if the two writes are happening on > > different devices. > > But the bio layer can manage it, by sending a write barrier down all relevant > queues. We can send a zero length write barrier command, yes?
Sort of --- there are various flush commands we can use. However, bio can't just submit the barriers, it needs to synchronise them, and that means doing a global wait over all the devices until they have all acked their barrier op. That's expensive: you may be as well off just using the current fs-internal synchronous commands at that point.
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