Messages in this thread | | | Date | Fri, 24 Oct 2003 11:36:35 +0200 | Subject | Re: [PATCH] ide write barrier support | From | Helge Hafting <> |
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On Thu, Oct 23, 2003 at 07:20:39PM +0200, Daniel Phillips wrote: > These are essentially the same, they both rely on draining the downstream > queues. But if we could keep the downstream queues full, bus transfers for > post-barrier writes will overlap the media transfers for pre-barrier writes, > which would seem to be worth some extra effort. > > To keep the downstream queues full, we must submit write barriers to all the > downstream devices and not wait for completion. That is, as soon as a > barrier is issued to a given downstream device we can start passing through > post-barrier writes to it. > This approach may fail:
a. Some pre-barrier writes go to all devices b. barrier is sent to all devices c. Post-barrier writes go to all devices d. drive 1 commits all its pre-barrier writes, then commits its post-barrier writes. e. drive 2 is slow and havent done the pre-barrier writes yet f. power is lost - leaving inconsistent devices.
The problem is that drive 1 don't know wether drive 2 did the barrier yet.
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