Messages in this thread | | | Date | Tue, 23 May 2006 15:23:31 +0200 (MEST) | From | Jan Engelhardt <> | Subject | Re: XFS write speed drop |
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>> CASE 1: Copying from one disk to another >> ======================================== >> Copying a compiled 2.6.17-rc4 tree; 306907 KB in 28566 files in 2090 >> directories. > >OK, we can call this a metadata intensive workload - lots of small >files, lots of creates. Barriers will hurt the most here, as we'd >already have been log I/O bound most likely, and I'd expect barriers >to only slow that further. > Yes and the most important thing is that someone made -o barrier the default and did not notice. Someone else? :-D
>Yep, note the user/sys shows no change, we're basically IO bound in >both tests, and barriers are hurting (as expected).
>> CASE 2: Removing >> ================ >> Remove the copies we created in case 1. >> >> 15:45 (none):/tmp # mount /dev/hdc2 /D -o barrier >> 15:45 (none):/D # time rm -Rf kernel-0 >> real 3m31.901s >> user 0m0.050s >> sys 0m3.140s > >versus: > >> 15:49 (none):/ # mount /dev/hdc2 /D -o nobarrier >> 15:49 (none):/D # time rm -Rf kernel-1 >> >> real 0m53.471s >> user 0m0.070s >> sys 0m1.990s >> 15:50 (none):/D # cd / >> 15:50 (none):/ # umount /D > >Also metadata intensive, of course. All the same issues as above, >and the same techniques should be used to address it. > >Odd that the system time jumped here. Roughly the same decrease in >performance though (3-4x).
You may, or may not, take that serious. I only ran each test once (since 3m31s vs 53s shows "enough" of the issue).
>So, I agree, you're seeing the cost of write barriers here, but I >don't see anything unexpected (unfortunately for you, I guess). > >The FAQ entry above will explain why they're enabled by default. >Try the v2 log change I suggested, hopefully that will mitigate >the problem somewhat. Alternatively, buy some decent hardware if >you're after performance. ;) > Well as mentioned, -o nobarrier solved it, and that's it. I do not actually need barriers (or an UPS, to poke on another thread), because power failures are rather rare in Germany.
Jan Engelhardt -- - 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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