On Thu, Jul 01, 2010 at 02:32:43PM +0200, Peter Zijlstra wrote:

On Thu, 2010-07-01 at 14:55 +0300, Michael S. Tsirkin wrote:

quoted

quoted

 - why can't it set the kernel thread's affinity too?

It can. However: the threads are started internally by the driver
when qemu does an ioctl.  What we want to do is give it a sensible
default affinity. management tool can later tweak it if it wants to.

So have that ioctl return the tid of that new fancy thread and then set
its affinity, stuff it in cgroup, whatever you fancy.

quoted

quoted

 - what happens if someone changes the tasks' affinity?

We would normally create a cgroup including all internal
tasks, making it easy to find and change affinity for
them all if necessary. 

And to stuff them in a cgroup you also need the tid, at which point it
might as well set the affinity from userspace, right?

We also put it in a cgroup transparently. I think that it's actually
important to do it on thread creation: if we don't, malicious userspace
can create large amount of work exceeding the cgroup limits.

And the same applies so the affinity, right? If the qemu process
is limited to a set of CPUs, isn't it important to make
the kernel thread that does work our behalf limited to the same
set of CPUs?

-- 
MST