Messages in this thread | | | Date | Tue, 3 May 2011 10:23:21 +0200 | From | Tejun Heo <> | Subject | Re: [PATCH 1/2]block: optimize non-queueable flush request drive |
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Hello,
On Tue, May 03, 2011 at 02:44:31PM +0800, Shaohua Li wrote: > > As I've said several times already, I really don't like this magic > > being done in the completion path. Can't you detect the condition on > > issue of the second/following flush and append it to the running list? > > hmm, don't understand it. blk_flush_complete_seq is called when the > second flush is issued. or do you mean do this when the second flush is > issued to disk? but when the second flush is issued the first flush is > already finished.
Ah, okay, my bad. That's the next sequence logic, so the right place. Still, please do the followings.
* Put it in a separate patch.
* Preferably, detect the actual condition (back to back flush) rather than the queueability test unless it's too complicated.
* Please make pending/running paths look more symmetrical.
> > If you already have tried that but this way still seems better, can > > you please explain why? > > > > Also, this is a separate logic. Please put it in a separate patch. > > The first patch should implement queue holding while flushing, which > > should remove the regression, right? > > ok. holding queue has no performance gain in my test, but it reduced a > lot of request requeue.
No, holding the queue should remove the regression completely. Please read on.
> > Hmmm... why do you need separate ->flush_exclusive_running? Doesn't > > pending_idx != running_idx already have the same information? > > when pending_idx != running_idx, flush request is added into queue tail, > but this doesn't mean flush request is dispatched to disk. there might > be other requests in the queue head, which we should dispatch. And flush > request might be reqeueud. Just checking pending_idx != running_idx will > cause queue hang because we thought flush is dispatched and then hold > the queue, but actually flush isn't dispatched yet, the queue should > dispatch other normal requests.
Don't hold elv_next_request(). Hold ->elevator_dispatch_fn().
Thanks.
-- tejun
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