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.pear...@hpe.com , enhanced/verified by linbao.zh...@hpe.com 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
