Messages in this thread | | | From | "Eff Norwood" <> | Subject | 2.4.18 *large* amount of time context switching | Date | Thu, 10 Oct 2002 17:52:16 -0700 |
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Hi All,
I have a 2.4.18 kernel running on a dual 2.4Ghz Xeon platform using software RAID 5 via IBM's EVMS and EXT3. The system is being used as an NFS server and although local disk performance is excellent, NFS performance (over UDP and TCP, vers 2 and 3 with multiple different client mount block sizes) is poor to bad. Looking at mpstat while the system is under load shows the %system to be quite high (94-96%) but most interestingly shows the number of intr/s (context switches) to be 17-18K plus!
Since I was not sure what was causing all of these context switches, I installed SGI kernprof and ran it during a 15 minute run. I used this command to start kernprof: 'kernprof -r -d time -f 1000 -t pc -b -c all' and this one to stop it: 'kernprof -e -i | sort -nr +2 | less > big_csswitch.txt'
The output of this collection is located here (18Kb):
http://www.effrem.com/linux/kernel/dev/big_csswitch.txt
Most interesting to me is why in the top three results:
default_idle [c010542c]: 861190 _text_lock_inode [c015d031]: 141795 UNKNOWN_KERNEL [c01227f0]: 101532
that default_idle would be the highest value when the CPUs showed 94-96% busy. Also interesting is what UNKNOWN_KERNEL is. ???
The server described above has 14 internal IDE disks configured as software Raid 5 and connected to the network with one Syskonnect copper gigabit card. I used 30 100 base-T connected clients all of which performed sequential writes to one large 1.3TB volume on the file server. They were mounted NFSv2, UDP, 8K r+w size for this run. I was able to achieve only 35MB/sec of sustained NFS write throughput. Local disk performance (e.g. dd file) for sustained writes is *much* higher. I am using knfsd with the latest 2.4.18 Neil Brown fixes from his site. Distribution is Debian 3.0 Woody Stable.
Many thanks in advance for the insight,
Eff Norwood
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