Messages in this thread | | | Subject | 2.6.1 slower than 2.4, smp/scsi/sw-raid/reiserfs | From | Philip Martin <> | Date | Sun, 01 Feb 2004 21:34:06 +0000 |
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The machine is a dual P3 450MHz, 512MB, aic7xxx, 2 disk RAID-0 and ReiserFS. It's a few years old and has always run Linux, most recently 2.4.24. I decided to try 2.6.1 and the performance is disappointing.
My test is a software build of about 200 source files (written in C) that I usually build using "nice make -j4". Timing the build on 2.4.24 I typically get something like
242.27user 81.06system 2:44.18elapsed 196%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (1742270major+1942279minor)pagefaults 0swaps
and on 2.6.1 I get
244.08user 116.33system 3:27.40elapsed 173%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+3763670minor)pagefaults 0swaps
The results are repeatable. The user CPU is about the same for the two kernels, but on 2.6.1 the elapsed time is much greater, as is the system CPU. I note a big difference in the pagefaults between 2.4 and 2.6 but I don't know what to make of it.
Comparing /proc/scsi/aic7xxx/0 before and after the build I see another difference, the "Commands Queued" to the RAID disks are much greater for 2.6 than 2.4
disk0 disk2 2.4 before: 8459 4766 after: 13798 7351
2.6 before: 21287 8555 after: 40491 15995
(The root partition is also on disk0 and that's not part of the RAID array; I guess that's why disk0 has higher numbers than disk2.)
The machine has another disk that is not part of the RAID array, it's a slower disk but I think the build is CPU bound anyway. I put an ext2 filesystem on this extra disk, and then used that for my trial build with the rest of the system, gcc, as, ld, etc. still coming from RAID array. On 2.4 the time for the ext2 build is essentially the same as for the RAID build, the difference is within the normal variation between builds. On 2.6 the ext2 build takes
244.43user 111.75system 3:16.42elapsed 181%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+3757151minor)pagefaults 0swaps
Although the CPU used is about the same as the RAID build the elapsed time is less, so there is some improvement but it is still worse than 2.4.24.
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