Messages in this thread | | | Date | Thu, 08 May 2003 23:53:34 +1000 | From | Nick Piggin <> | Subject | Re: Q: Anticipatory scheduler docs |
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Szonyi Calin wrote:
>Hello everyone > >Where can I find documentation about the anticipatory scheduler >and about tuning it ? > Ahh heh... when I write them :P Seriously, its been under quite a bit of work, I've tried to keep some docs up to date but its not worth it at the moment. Its getting more stable now, but I have some auto tuning stuff on the cards which changes things again...
Anyway in brief there are 5 parameters under /sys/block/*/iosched/ all are set in milliseconds. * read_expire Controls how long until a request becomes "expired". It also controls the interval between which expired requests are served, so set to 50, a request might take anywhere < 100ms to be serviced _if_ it is the next on the expired list. Obviously it can't make the disk go faster. Result is basically the timeslice a reader gets in the presence of other IO. 100*((seek time / read_expire) + 1) is very roughly the % streaming read efficiency your disk should get in the presence of multiple readers. * read_batch_expire Controls how much time a batch of reads is given before pending writes are served. Higher value is more efficient. Shouldn't really be below read_expire. * write_ versions of the above * antic_expire Controls the maximum amount of time we can anticipate a good read before giving up. Many other factors may cause anticipation to be stopped early, or some processes will not be "anticipated" at all. Should be a bit higher for big seek time devices though not a linear correspondance - most processes have only a few ms thinktime.
Hows that? Let me know of any benchmark results you might happen upon.
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