RE: [PATCH v1 0/2] fix the defect that pcc-cpufreq's pcc_get_freq() sometimes can't get correct CPU frequency

[Zhang, Lin-Bao (Linux Kernel R&D)]

Hi all, 

About this patch , do you have any comments ?  
Thanks for your any comments , corrections and etc. 

Thanks very much!

Followings are last emails :
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-Bob


> -----Original Message-----
> From: Zhang, Lin-Bao (Linux Kernel R&D)
> Sent: 2015年11月16日 18:36
> To: 'rjw@xxxxxxxxxxxxx'; 'viresh.kumar@xxxxxxxxxx'; 'linux-pm@xxxxxxxxxxxxxxx';
> 'linux-kernel@xxxxxxxxxxxxxxx'
> Subject: [PATCH v1 0/2] fix the defect that pcc-cpufreq's pcc_get_freq()
> sometimes can't get correct CPU frequency
> 
> 
> Summary :
> 
> These 2 patches are developed for drivers/cpufreq/pcc-cpufreq.c's
> pcc_get_freq() function.
> The pcc-cpufreq driver's function pcc_get_freq() sometimes returns invalid
> frequency information.
> Without the these 2 patches , it can be reproduced on booting Linux Kernel with
> loading pcc-cpufreq.ko and loop unloading/loading pcc-cpufreq.ko.
> This problem has been reported on ProLiant systems, primarily 4-socket systems,
> for example DL580Gen8.
> 
> Generally speaking, as PCC spec,patch 1 can ideally ensure to get correct cpu
> freqency if FW works well.
> if it fails, patch 2 can be run to retry 2 times to get cpu freq as workaround.
> 
> These 2 patches are written by HP's greg.pearson@xxxxxxx , enhanced/verified
> by Linbao.zhang@xxxxxxx
> 
> PATCH 1/2:
> in Processor Clocking Control specification v1.0 ,there are 2 limitations :
> 2.1.8 Minimum Time Between Commands
> 2.1.9 Maximum Time Between Commands
> that means 2 commands' interval should be located between Minimum Time
> Between Commands and Maximum
> 
> Time Between Commands.
> this patch implements this feature,while old pcc-cpufreq.c didn't strictly follow
> the spec.
> ideally , this patch ensure pcc_get_freq() return valid freq based on the fact FW
> is working well.
> 
> PATCH 2/2:
> if pcc_get_freq() returns 0, we will retry 2 times at most. This is a workaround
> patch, although it is 100% perfect.This works around a firmware/timing issue. In
> very rare case , it also will fail after retrying 2 times due to firmware issue. Based
> on current pcc cpufreq design , this workaround would be the best solution by
> confirmation with FW guys. patch 2 has been adoted by sles11sp4.
> 
> Detailed testing data can be found as following :
> 
> our testing result on DL580Gen8 with upstream kernel:
> a) loop unloading/loading pcc driver within 14 hours , pcc_get_freq() always
> succeed , the patch always succeeded, don't need the second patch to
> workaround
> b) loop rebooting DL580Gen8 with git kernel: by writting a shell script, found
> about rebooting 200+ times, patch 1 and patch 2 may both failed once, means
> pcc_get_freq() returns 0 frequency,although its possibility is very very low.
> pcc_get_freq() doesn't affect pcc-cpufreq driver loading ,because they are
> running different path.
> in this loop rebooting test , pcc-cpufreq can always be loaded successfully.
> 
> We can say ,patch 1 and patch 2 would be the best solution for this issue.
> 
> Zhang Lin-Bao (2):
>   enforce max/min time between commands
>   retry 2 times when getting cpu frequency is zero
> 
>  drivers/cpufreq/pcc-cpufreq.c | 51
> ++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 50 insertions(+), 1 deletion(-)
> 
> --
> 1.8.5.2
>