On Thu, 30 Oct, at 11:47:40PM, Peter Zijlstra wrote:
Let me reply to just this one, I'll do the rest tomorrow, need sleeps.
On Thu, Oct 30, 2014 at 06:22:36PM -0400, Tejun Heo wrote:
This controller might not even require the distinction between
configured and effective tho? Can't a new child just inherit the
parent's configuration and never allow the config to become completely
empty?
It can do that. But that still has a problem, there is a mapping in
hardware which restricts the number of active configurations. The total
configuration space is larger than the supported active configurations.
So _something_ must fail. The initial proposal was mkdir failing when
there were more than the hardware supported active config cgroup
directories. The alternative was on-demand activation where we only
allocate the hardware resource when the first task gets moved into the
group -- which then clearly can fail.
Hmmm... why can't it just refuse creating a different configuration
when its config space is full? Make children inherit the parent's
configuration and refuse config writes which require it to create a
new one if the config space is full. Seems pretty straight-forward.
What am I missing?
We could do that I suppose, there is the one corner case that would not
allow, intermediate directories with a restricted config that also have
priv restrictions but no actual tasks. Not sure that makes sense though.
Could you elaborate on this configuration?
Are there any other cases I might have missed?
I don't think so.
So, for the specific CAT case what you're proposing is make the failure
case happen when writing to the cache bitmask file instead of failing
mkdir() or echo $tid > tasks ?
I think that's OK. If we've run out of CLOS ids I would expect to see
-ENOSPC returned, whereas if we try and set an invalid bitmask we'd get
-EINVAL.
Vikas, Will?
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Matt Fleming, Intel Open Source Technology Center