* context switches and responsiveness
@ 2009-05-26 8:32 Antoine Martin
2009-05-26 9:05 ` Avi Kivity
0 siblings, 1 reply; 6+ messages in thread
From: Antoine Martin @ 2009-05-26 8:32 UTC (permalink / raw
To: kvm@vger.kernel.org
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Hi,
I've recently increased the number of guests (+20%) running on one of my
hosts and found that the responsiveness suffered.
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?
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??
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
root=/dev/vda elevator=noop -nographic -drive
file=./vm/root_fs,if=virtio,boot=on -net
nic,vlan=14,macaddr=fe:f0:00:00:00:0e,model=virtio -net
tap,vlan=14,ifname=tap14,script=no
Cheers
Antoine
- ----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
9 20 71 0 0 0| 0 0 | 270B 567B| 0 0 | 20k 29k
17 16 66 1 0 0|8192B 1776k| 548B 876B| 0 0 | 20k 31k
8 17 75 0 0 0| 0 336k| 927B 1291B| 0 0 | 20k 29k
13 16 71 0 0 0| 0 1088k|1422B 8505B| 0 296k| 20k 31k
23 14 63 0 0 0| 0 0 |3918B 3058B| 0 0 | 19k 33k
11 16 71 0 0 0|8192B 1120k| 132B 534B| 0 0 | 19k 30k
16 18 66 0 0 0| 0 32k| 330B 7662B| 0 0 | 19k 30k
13 18 69 0 0 0| 0 128k| 264B 420B| 0 0 | 19k 31k
16 17 66 0 0 0| 0 240k| 474B 420B| 0 0 | 19k 30k
11 21 68 0 0 0| 0 1648k| 372B 4196B| 0 0 | 20k 32k
13 18 69 0 0 0| 0 96k| 708B 500B| 0 0 | 20k 30k
15 19 66 0 0 0| 0 256k| 66B 322B| 0 0 | 20k 30k
15 22 63 0 0 0| 0 32k| 804B 8906B| 0 0 | 20k 31k
14 19 67 0 0 0|8192B 256k| 838B 590B|4096B 0 | 19k 31k
13 16 71 0 0 0| 0 0 | 132B 534B| 0 0 | 20k 31k
16 18 62 4 0 0| 312k 976k| 396B 7872B| 156k 0 | 20k 32k
13 22 65 0 0 0| 0 352k| 573B 534B| 0 0 | 19k 31k
14 20 67 0 0 0| 0 160k| 304B 696B| 0 0 | 19k 31k
12 12 74 0 1 0| 0 512k| 514B 4268B| 0 0 | 19k 31k
10 19 72 0 0 0| 0 152k| 290B 420B| 0 0 | 19k 31k
14 18 67 2 0 0| 16k 232k| 224B 306B| 0 0 | 19k 31k
20 23 57 0 0 0| 0 80k|1898B 5544B| 0 0 | 20k 32k
14 14 72 0 0 0| 0 112k|2286B 2482B| 0 0 | 20k 32k
18 17 65 0 0 0| 0 176k|1057B 1169B| 0 0 | 20k 31k
15 13 72 0 0 0| 0 144k| 422B 7614B| 0 0 | 19k 31k
11 15 72 0 0 0| 0 944k| 448B 436B| 0 0 | 19k 31k
9 18 73 0 0 0| 0 1584k| 266B 348B| 0 0 | 19k 33k
15 17 68 0 0 0| 0 0 | 721B 7646B| 0 0 | 20k 31k
14 20 66 0 0 0| 0 0 | 356B 420B| 0 0 | 20k 31k
16 15 69 0 0 0| 0 432k| 532B 420B| 0 0 | 19k 31k
14 18 68 0 0 0| 0 144k| 628B 4058B| 0 0 | 19k 30k
10 20 71 0 0 0| 0 160k| 316B 486B| 0 0 | 20k 31k
11 17 72 0 0 0| 0 80k| 266B 462B| 0 0 | 20k 31k
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: context switches and responsiveness
2009-05-26 8:32 context switches and responsiveness Antoine Martin
@ 2009-05-26 9:05 ` Avi Kivity
2009-05-26 9:37 ` context switches and responsiveness [SOLVED] Antoine Martin
0 siblings, 1 reply; 6+ messages in thread
From: Avi Kivity @ 2009-05-26 9:05 UTC (permalink / raw
To: Antoine Martin; +Cc: kvm@vger.kernel.org
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: context switches and responsiveness [SOLVED]
2009-05-26 9:05 ` Avi Kivity
@ 2009-05-26 9:37 ` Antoine Martin
2009-05-26 9:39 ` Avi Kivity
0 siblings, 1 reply; 6+ messages in thread
From: Antoine Martin @ 2009-05-26 9:37 UTC (permalink / raw
To: Avi Kivity; +Cc: kvm@vger.kernel.org
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Hash: SHA512
> Ah, -usbdevice tablet, interrupt generator from hell. Let it go and
> you'll see your context switch rate drop.
Indeed that solved it!
(only kept it for the one windows guest that really needs it)
Many many thanks.
>> - ----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
New (healthy) dstat with 10 guests running:
- ----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system--
usr sys idl wai hiq siq| read writ| recv send| in out | int csw
2 1 92 5 0 0| 0 80k| 87k 88k| 0 0 |1222 2567
1 1 98 0 0 0| 0 0 | 89k 89k| 0 0 |1230 2618
What a difference this tablet makes!!
Antoine
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: context switches and responsiveness [SOLVED]
2009-05-26 9:37 ` context switches and responsiveness [SOLVED] Antoine Martin
@ 2009-05-26 9:39 ` Avi Kivity
2009-05-26 9:41 ` Antoine Martin
0 siblings, 1 reply; 6+ messages in thread
From: Avi Kivity @ 2009-05-26 9:39 UTC (permalink / raw
To: Antoine Martin; +Cc: kvm@vger.kernel.org
Antoine Martin wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA512
>
>
>> Ah, -usbdevice tablet, interrupt generator from hell. Let it go and
>> you'll see your context switch rate drop.
>>
> Indeed that solved it!
> (only kept it for the one windows guest that really needs it)
> Many many thanks.
>
Why do you need it? vnc? Switching to a better vnc client (I use
vinagre) may allow you to drop it.
--
error compiling committee.c: too many arguments to function
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: context switches and responsiveness [SOLVED]
2009-05-26 9:39 ` Avi Kivity
@ 2009-05-26 9:41 ` Antoine Martin
2009-05-26 10:01 ` Avi Kivity
0 siblings, 1 reply; 6+ messages in thread
From: Antoine Martin @ 2009-05-26 9:41 UTC (permalink / raw
To: Avi Kivity; +Cc: kvm@vger.kernel.org
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Hash: SHA512
Avi Kivity wrote:
> Antoine Martin wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA512
>>
>>
>>> Ah, -usbdevice tablet, interrupt generator from hell. Let it go and
>>> you'll see your context switch rate drop.
>>>
>> Indeed that solved it!
>> (only kept it for the one windows guest that really needs it)
>> Many many thanks.
>>
>
> Why do you need it? vnc?
Yes.
> Switching to a better vnc client (I use
> vinagre) may allow you to drop it.
I thought I had tried them all in desperation (mouse going out of sync),
I'll try again.
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: context switches and responsiveness [SOLVED]
2009-05-26 9:41 ` Antoine Martin
@ 2009-05-26 10:01 ` Avi Kivity
0 siblings, 0 replies; 6+ messages in thread
From: Avi Kivity @ 2009-05-26 10:01 UTC (permalink / raw
To: Antoine Martin; +Cc: kvm@vger.kernel.org
Antoine Martin wrote:
>> Switching to a better vnc client (I use
>> vinagre) may allow you to drop it.
>>
> I thought I had tried them all in desperation (mouse going out of sync),
> I'll try again.
>
Vinagre does mouse capture like SDL. It isn't perfect, but much better
than the standard vnc client.
--
error compiling committee.c: too many arguments to function
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2009-05-26 10:02 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2009-05-26 8:32 context switches and responsiveness Antoine Martin
2009-05-26 9:05 ` Avi Kivity
2009-05-26 9:37 ` context switches and responsiveness [SOLVED] Antoine Martin
2009-05-26 9:39 ` Avi Kivity
2009-05-26 9:41 ` Antoine Martin
2009-05-26 10:01 ` Avi Kivity
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