Re: PATCH - update TSC freq when cpufreq changes it

Max Laier wrote:
On Tuesday 27 February 2007 23:16, Nate Lawson wrote:
Attached is a patch that uses eventhandlers to update the TSC freq.
This is important because DELAY() uses TSC directly (on i386 and amd64)
but the rate calculated at boot changes if cpufreq is in use.

It maintains current behavior that cpufreq transitions are denied if
TSC is the active timecounter. The API is that there is a pre and post
transition eventhandler that is called by the cpufreq core. The pre
handler is passed the next state (including freq, power, etc.) and can
store a non-zero status value in the output arg to indicate it wants to
reject the transition. The post handler also is passed the next state
and the result of the transition (0 on success).

Any reason for passing the result to the post handler in by reference -
other than being able to re-use the same function type as in the pre
handler? API-wise this seems to be a mistake as one consumer could mess
up the result for the rest and the variable name "error" in the INVOKE
also suggests that this could be used to report back.

Yes, the main gaol was to reuse the function. Plus I thought in the
future there might be some conceivable need to revoke a change after it
had occurred ("oops! change right back!"). We wouldn't need to change
an API to allow that.

Unless there's a real problem with it, I'd like to keep that ability in
the API. To make it clear though, I should probably assign error to
some tmp var and pass that in to cpufreq_post_change handlers so it has
no effect if the user overwrites it.

--
Nate
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Relevant Pages

  • Re: PATCH - update TSC freq when cpufreq changes it
    ... but the rate calculated at boot changes if cpufreq is in use. ... transition eventhandler that is called by the cpufreq core. ... Any reason for passing the result to the post handler in by reference - ...
    (freebsd-arch)
  • Re: PATCH - update TSC freq when cpufreq changes it
    ... but the rate calculated at boot changes if cpufreq is in use. ... transition eventhandler that is called by the cpufreq core. ... Any reason for passing the result to the post handler in by reference - ...
    (freebsd-current)
  • Re: PATCH - update TSC freq when cpufreq changes it
    ... but the rate calculated at boot changes if cpufreq is in use. ... transition eventhandler that is called by the cpufreq core. ... The post handler also is passed the next state ... Any reason for passing the result to the post handler in by reference - ...
    (freebsd-current)