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Date: Fri, 30 Mar 2007 06:22:21 +0800
From: "Elliott Johnson" <ejohnson@...uxmail.org>
To: linux-kernel@...r.kernel.org
Subject: strange high system cpu usage.
Hello,
I've been upgrading a few machines here at work and noticed some problems with high system cpu usage on one machine. In trying to debug the problem I've come across a few confusing stats that I was hoping could be cleared up by someone on this list.
Firstly some info about the system. It's a dell 2850 running a 32bit gentoo install with glibc 2.5 and kernel 2.6.19. A single multi-threaded process is generating the system cpu usage. One of our developers wrote the code and it does some intense disk reads and writes, which should create primarily iowait cpu usage. On a debian system with the same hardware using glibc-2.4 and kernel 2.6.8 the process generates virtually 0 load compared the the upgraded server's load of 2-4.
Here is some disk usage info:
dc2 linux # sar -d -p
17:40:01 DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util
17:45:01 sda 0.61 10.50 5.11 25.47 0.00 1.07 0.91 0.06
17:45:01 sdb 26.43 41.81 438.41 18.17 0.19 7.10 2.42 6.41
17:45:01 nodev 26.63 41.81 438.41 18.03 0.19 7.07 2.41 6.41
17:50:01 sda 0.10 0.35 0.97 13.66 0.00 0.28 0.28 0.00
17:50:01 sdb 25.45 56.05 523.54 22.77 0.06 2.38 1.88 4.80
17:50:01 nodev 25.67 56.05 523.54 22.58 0.06 2.38 1.87 4.79
Here is some cpu info:
dc2 linux # sar -p
17:40:01 CPU %user %nice %system %iowait %steal %idle
17:45:01 all 0.05 0.00 20.80 0.27 0.00 78.89
17:50:01 all 0.03 0.00 26.46 0.24 0.00 73.26
Here are some memory stats:
dc2 linux # vmstat 3
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
2 0 0 1166088 320 720204 0 0 14 63 131 124 0 23 76 0
0 0 0 1165832 320 720808 0 0 32 410 400 253 0 30 70 0
1 0 0 1165028 320 721208 0 0 16 260 469 297 0 22 78 0
1 0 0 1164228 320 722156 0 0 141 59 474 340 0 27 71 2
dc2 linux # vmstat -s
2075276 total memory
993380 used memory
162412 active memory
697456 inactive memory
1081896 free memory
320 buffer memory
792036 swap cache
4152792 total swap
0 used swap
4152792 free swap
1308 non-nice user cpu ticks
0 nice user cpu ticks
286057 system cpu ticks
951507 idle cpu ticks
3378 IO-wait cpu ticks
188 IRQ cpu ticks
362 softirq cpu ticks
0 stolen cpu ticks
157581 pages paged in
780844 pages paged out
0 pages swapped in
0 pages swapped out
1617473 interrupts
1506805 CPU context switches
1175215011 boot time
7709 forks
We rebooted it a few moments ago, but before that vmstat showed that the buffered memory was 0kb. This is very different from the other machine which has around 500Mb. A low buffer mem count seems common in our machines with kernel 2.6.17-2.6.19. Looking at vmstat's man page its difficult to understand exactly what buffered mem is and how to go about altering things to get this value higher to test with. It seems to be a computed value and not something settable via /proc. Does any one know more about buffered memory and how to adjust it?
-Elliott Johnson
=
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