Messages in this thread |  | | | From | "D. Jansen" <> | | Date | Mon, 30 May 2011 23:24:03 +0200 | | Subject | Re: [rfc] Ignore Fsync Calls in Laptop_Mode |
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On Mon, May 30, 2011 at 10:53 PM, <david@lang.hm> wrote: > On Mon, 30 May 2011, D. Jansen wrote: > >> On Mon, May 30, 2011 at 8:45 PM, <david@lang.hm> wrote: >>> >>> >>> the problem is that most users don't know what their system is running, >>> or >>> what effect disaling fsync would have. those that do can probably use >>> LD_PRELOAD to override fsync calls. >> >> As we found out, they can't. But if we export barrier, I hope a >> library could wrap fsyncs into barriers. Is that the case? > > a library can wrap fsync into anything. > >>> >>> it doesn't take running a mail server, even a mail client will have the >>> same >>> risk. If you use POP for mail (a very common option) then you download >>> messages and tell the server to delete them. if you do not really save >>> them >>> (one fsync after they are all saved), then you can loose everything that >>> you >>> downloaded. >> >> Yes, I know. It's the same argument again and again. I understand not >> everybody wants this. But some do. Some prefer working 10-20% longer >> on battery (certainty) instead of possibly losing 5 % data >> (possibility) or losing all your data (possibility if you use laptop >> mode and the hard disk wakes up again and again and eventually wears >> out). > > those are some powerful numbers you are throwing around, can you back them > up?
Yes. My netbook uses 4.8 W with hard disk off. 0.5 W more with hard disk on. A lot of the time, the display is off and the power consumption drops to about 3.5 W. I don't know how I got to 20 % atm. I can only do this if fsync is disabled. I tried before, but it would go on for every write. It died, very prematurely. > > do you really have so many fsync's going on that the disk spins up so much > that you would gain 10-20% battery life?
Yes. Every autosave in LibreOffice triggers one. And I want autosave, but I want them in memory, not on disk. > > and what makes you think the extra spin-ups from fsyncs will cause your hard > drive to fail significantly earlier? (if you have a hard drive with a > limited number of spin-up cycles, you probably don't want to use laptop mode > at all)
Experience, see above. Also, this is well described behavior. All hard disks are only designed to last a certain number of head loads and unloads. Spinning up and down even less. > > why do you think it's a possibility of loosing only 5% of data?
Well, it really depends on the way your configure laptop mode. But in my case the laptop mode window is 20 minutes, the run time then is about 10-12 hrs. I can actually lose less than 5 % of the data created during the battery run time. It's a certain 1-1.5 hours (10-15 %) more work or a possible 20 mins (3.3 % actually) loss of work. I think it's a good deal. -- 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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