Messages in this thread | | | Subject | Re: [patch]cfq-iosched: delete deep seeky queue idle logic | From | Shaohua Li <> | Date | Mon, 26 Sep 2011 08:51:39 +0800 |
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On Fri, 2011-09-23 at 21:24 +0800, Vivek Goyal wrote: > On Wed, Sep 21, 2011 at 07:16:20PM +0800, Shaohua Li wrote: > > [..] > > > Try a workload with one shallow seeky queue and one deep (16) one, on > > > a single spindle NCQ disk. > > > I think the behaviour when I submitted my patch was that both were > > > getting 100ms slice (if this is not happening, probably some > > > subsequent patch broke it). > > > If you remove idling, they will get disk time roughly in proportion > > > 16:1, i.e. pretty unfair. > > I thought you are talking about a workload with one thread depth 4, and > > the other thread depth 16. I did some tests here. In an old kernel, > > without the deep seeky idle logic, the threads have disk time in > > proportion 1:5. With it, they get almost equal disk time. SO this > > reaches your goal. In a latest kernel, w/wo the logic, there is no big > > difference (the 16 depth thread get about 5x more disk time). With the > > logic, the depth 4 thread gets equal disk time in first several slices. > > But after an idle expiration(mostly because current block plug hold > > requests in task list and didn't add them to elevator), the queue never > > gets detected as deep, because the queue dispatch request one by one. > > When the plugged requests are flushed, then they will be added to elevator > and at that point of time queue should be marked as deep? The problem is there are just 2 or 3 requests are hold to the per-task list and then get flushed into elevator later, so the queue isn't marked as deep.
> Anyway, what's wrong with the idea I suggested in other mail of expiring > a sync-noidle queue afer few reuqest dispatches so that it does not > starve other sync-noidle queues. The problem is how many requests a queue should dispatch. cfq_prio_to_maxrq() == 16, which is too many. Maybe use 4, but it has its risk. seeky requests from one task might be still much far way with requests from other tasks.
Thanks, Shaohua
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