Messages in this thread | | | Subject | Re: RFC on io-stalls patch | From | Chris Mason <> | Date | 11 Jul 2003 10:13:24 -0400 |
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On Thu, 2003-07-10 at 09:57, Jens Axboe wrote: > On Tue, Jul 08 2003, Marcelo Tosatti wrote: > > > > Hello people, > > > > To get better IO interactivity and to fix potential SMP IO hangs (due to > > missed wakeups) we, (Chris Mason integrated Andrea's work) added > > "io-stalls-10" patch in 2.4.22-pre3. > > > > The "low-latency" patch (which is part of io-stalls-10) seemed to be a > > good approach to increase IO fairness. Some people (Alan, AFAIK) are a bit > > concerned about that, though. > > > > Could you guys, Stephen, Andrew and maybe Viro (if interested :)) which > > havent been part of the discussions around the IO stalls issue take a look > > at the patch, please? > > > > It seems safe and a good approach to me, but might not be. Or have small > > "glitches". > > Well, I have one naive question. What prevents writes from eating the > entire request pool now? In the 2.2 and earlier days, we reserved the > last 3rd of the requests to writes. 2.4.1 and later used a split request > list to make that same guarentee. > > I only did a quick read of the patch so maybe I'm missing the new > mechanism for this. Are we simply relying on fair (FIFO) request > allocation and oversized queue to do its job alone?
Seems that way. With the 2.4.21 code, a read might easily get a request, but then spend forever waiting for a huge queue of merged writes to get to disk.
I believe the new way provides better overall read performance in the presence of lots of writes.
-chris
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