Messages in this thread | | | Date | Thu, 14 Aug 2003 13:02:50 -0700 (PDT) | From | markw@osdl ... | Subject | Re: bounce buffers and i/o schedulers with aacraid |
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On 13 Aug, Andrew Morton wrote: > markw@osdl.org wrote: >> >> We're still trying to avoid bounce buffers with the aacraid driver and >> noticed something interesting in some profiles (which I'll copy farther >> down) with the deadline scheduler and AS. Using our DBT-2 workload, we >> see with the deadline scheduler our patch to avoid bounce buffers >> doesn't change the profile much. But with AS, we don't see >> bounce_copy_vec or __blk_queue_bounce near the top of the profile. Any >> ideas why? > > It shouldn't make any difference. > > One thing to be careful about is to make sure that the pages which are > being put under I/O are in the same place across different tests. > > Suppose your machine already had 3G of pagecache and you then run the test. > You would magically find that newly allocated pages come out of > ZONE_NORMAL and no bouncing is needed for them. So the moral is to make > sure that the starting conditions are the same for each test: almost all > memory free.
I think we've tracked the problem to old firmware on the raid controllers we have. They'll be upgraded shortly.
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