[PATCH] transition latency of speedstep-ich

[Eric Piel <Eric.Piel@tremplin-utc.net>]

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Dominik Brodowski a écrit :
> On Sun, Feb 06, 2005 at 11:33:49PM +0100, Eric Piel wrote:
:
>>This patch proposes to consider a CPUFREQ_ETERNAL latency as the maximum 
>>possible latency of the governor (10 ms). I think this should be 
>>conservative enough to be safe with any driver.
>  
> No. CPUFREQ_ETERNAL is there to assert no dynamic frequency governor runs
> with this driver. If a driver is safe to run on dynamic frequency governors
> like ondemand, fix the latency value instead.
> 
OK, so here is a patch for vanilla 2.6.11 to set the transition latency 
of speedstep-ich (the only driver which I can test in addtion to 
p4-clockmod). Actually it was quite hard to find, the intel manual 
(29834006.pdf) doesn't assert this latency clearly. From what I 
understood the frequency transition could take up to about 40µs (p.44) 
while the voltage transition could take up to 100µs (p.22 and p.58). So 
I put 100µs as the transition latency of this driver.

I've tried it on my computer, it works, and the ondemand governor can 
now support my hardware!

Hope you like it,
Eric

--
Set the transition latency of speedstep-ich to 100µs as described in 
intel's manual.

Signed-off-by: Eric Piel <eric.piel@tremplin-utc.net>
--

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--- linux-2.6.11/arch/i386/kernel/cpu/cpufreq/speedstep-ich.c.orig	2005-02-07 23:52:55.000000000 +0100
+++ linux-2.6.11/arch/i386/kernel/cpu/cpufreq/speedstep-ich.c	2005-03-06 17:51:04.000000000 +0100
@@ -335,7 +335,8 @@
 
 	/* cpuinfo and default policy values */
 	policy->governor = CPUFREQ_DEFAULT_GOVERNOR;
-	policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
+ 	/* Max 100µs, according to intel's 29834006.pdf p.22 */
+	policy->cpuinfo.transition_latency = 100000;
 	policy->cur = speed;
 
 	result = cpufreq_frequency_table_cpuinfo(policy, speedstep_freqs);

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