oprofile

[Tim Yeung_1]

I ran oprofile on RHEL4U6 and got the following report. What does cache refer to? Is it referring to Linux memory cache or the processor L2 cache? Why is my system spending so much time in cache? Thanks.

CPU: P4 / Xeon with 2 hyper-threads, speed 3000.38 MHz (estimated)
Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped) with a unit mask of 0x01 (mandatory) count 100000
GLOBAL_POWER_E...|
samples| %|
------------------
14219190 78.5593 cache
2596696 14.3464 vmlinux
985675 5.4457 libc-2.3.4.so
116542 0.6439 oprofiled
105647 0.5837 tg3
67943 0.3754 oprofile
1601 0.0088 top
1253 0.0069 ext3
1064 0.0059 jbd
769 0.0042 libproc-3.2.3.so
713 0.0039 hald
613 0.0034 libncurses.so.5.4
443 0.0024 bash
428 0.0024 uhci_hcd
249 0.0014 ld-2.3.4.so
216 0.0012 ehci_hcd
121 6.7e-04 libcrypto.so.0.9.7a
113 6.2e-04 cciss
90 5.0e-04 libgobject-2.0.so.0.400.7
85 4.7e-04 qla2xxx

[Derek Whigham_1 · Accepted solution]

Just a guess , but you are using fibre channel drives (qla2xxx) driver. Correct?

I have seen huge cache hits. If the i/o to the FC drives is to high for the number of spindles attached to the LUN.

Run iostat to see the usage.

Are you using path management software (securepath , powerpath etc)

Looks to me that a LUN is max'd out.

[Tim Yeung_1]

No, we're not using SAN disks. We're using internal RAIDed disks in a DL580. But thanks for the hint. I'll check iostat.

[Tim Yeung_1]

No it wasn't disks being saturated. Turns out the application being run is called "cache". That's what it was!