Messages in this thread |  | | | Date | Sat, 26 Nov 2005 11:33:32 +0800 | | From | Wu Fengguang <> | | Subject | Re: [PATCH 16/19] readahead: laptop mode support |
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On Fri, Nov 25, 2005 at 05:06:25PM +0100, Bart Samwel wrote: > Wu Fengguang wrote: > >When the laptop drive is spinned down, defer look-ahead to spin up time. > > Just a n00b question: isn't readahead something that happens at read > time at the block device level? And doesn't the fact that you're reading > something imply that the drive is spun up? Or can readahead be triggered > by reading from cache?
Yes, both the old and new read-ahead logic issue read-ahead requests before the pages are immediately needed. It is called look-ahead in the new logic, which achieves I/O pipelining, and helps hide the I/O latency.
> >For crazy laptop users who prefer aggressive read-ahead, here is the way: > > > ># echo 1000 > /proc/sys/vm/readahead_ratio > ># blockdev --setra 524280 /dev/hda # this is the max possible value > > These amounts of readahead are absolutely useless though. I've done > measurements about a year ago, that show that at a spindown time of two > minutes you've basically achieved all the power savings you can get. > More than 10 minutes of spindown is absolutely useless unless you have a > desktop drive, because those don't normally support more than 50,000 > spinup cycles. The only apps I can think of that work on this amount of > data in such a short period of time are all apps where you shouldn't be > concerned about power drawn by the hard drive. :)
Thanks, I have read about the paper, quite informative :)
It's just that some one suggested about the feature, and it's just a matter of lifting some limit values in the code - so I did it :)
Regards, Wu - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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