Xen Scheduler Tweaking for Better Performance

I've been doing some research and have found that the Xen scheduler can be tweaked for better performance.  The Xen scheduler can be tweaked by adjusting the 'time slice" and "rate limit" variables in the scheduler.

Here is a write up on how the scheduler works:  http://wiki.xen.org/wiki/Credit_Scheduler

Based on this write up, the default time slice parameter of 30ms may not be the best choice.  I've been playing with these values and have found I can improve my Windows 7 Media Center operation on WMC Extenders when playing live TV.

I have several cable HD channels that have issues with live tv.  I can't figure out why only certain channels are affected, but I definitely can improve the operation by adjusting the Xen scheduler.

Use xl to show the current scheduler parameters:

# xl sched-credit
Cpupool Pool-0: tslice=30ms ratelimit=1000us
Name                                ID Weight  Cap
Domain-0                             0    256    0

I made adjustments for my situation that did help with the Windows 7 Media Center VM:

# xl sched-credit
Cpupool Pool-0: tslice=5ms ratelimit=2000us
Name                                ID Weight  Cap
Domain-0                             0    256    0

These parameters can be adjusted by the following xl commands:

Time Slice:

# xl sched-credit -s -t 5

Rate Limit:

[# xl sched-credit -s -r 2000

These changes can be made in the syslinux.cfg so they are set when booting in Xen.

append /xen sched_credit_tslice_ms=5 sched_ratelimit_us=2000 --- /bzimage --- /bzroot

The values I have chosen may not be the best for you, but this gives you the opportunity to do some tweaking to see if it works in your situation.