Antoine Martin wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 Hi, I've recently increased the number of guests (+20%) running on one of my hosts and found that the responsiveness suffered.
How many guests? How many vcpus?
Before that, the context switches were hovering around 10K, now they're close to 30K. Or this could just be because I upgraded the host kernel and kvm: host and guests are running 2.6.29.4 + kvm-86 Is there anything that can be done to reduce this? I thought dynticks would prevent unecessary context switching?
dynticks is the default IIRC. What type guests are you running? If Linux, make sure the guests are dynticks as well.
As you can see from the dstat sample below, the host can be very quiet at times, and yet the guests are a bit sluggish. (there is no swapping going on in the guests either) Is 30K context switches normal for a host that's mostly idle??
Depends on guest count! Please provide kvm_stat output.
Here is a sample guest command line: - -clock dynticks -usbdevice tablet -m 1024 -monitor telnet:127.0.0.1:10005,server,nowait -L ./ -kernel ./bzImage-2.6.29.4 - -append earlyprintk=serial,ttyS0,115200,keep console=ttyS0,115200
Ah, -usbdevice tablet, interrupt generator from hell. Let it go and you'll see your context switch rate drop.
- ----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system-- usr sys idl wai hiq siq| read writ| recv send| in out | int csw 14 15 71 0 0 0| 0 0 | 942B 6912B| 0 0 | 20k 29k 11 17 71 0 0 0| 0 160k| 460B 818B| 0 0 | 19k 30k
Interrupt rate is close to context switch rate, which is good. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
