Re: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree
- From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 30 Nov 2007 14:20:58 -0800
On Fri, 30 Nov 2007 14:06:55 -0800
"Pallipadi, Venkatesh" <venkatesh.pallipadi@xxxxxxxxx> wrote:
Please dont go off-list like this. I put Mark's original mailing list cc's
back.
I will have to Nack this. The reason max_cstate was initentionally
removed due to couple of reasons:
It broke userspace without any warning or migration period, afaict.
1) All in kernel users of max_cstate should rather be using
pm_qos/latency interfaces. All such max_cstate usages must already be
migrated.
That code isn't merged.
2) Supporting max_cstate as a dynamic parameter cleanly is no longer
possible in acpi/processor_idle.c as the C-state policy has moved to
cpuidle instead. It can be done if it is needed. But, just below patch
will not really work with cpuidle.
Selecting max_cstate at boot time as a debug option still works without
this patch.
So, just this patch will not get back the functionality with cpuidle.
Infact changing it at run time will have no effect. Question however is:
Is there a real need to revive this parameter so that user can change
max_cstate at run time?
It is not known whether Mark is actually writing to this thing. Perhaps
read-only permissions would be a suitable fix?
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