On Monday, September 26, 2016 11:15:45 AM Larry Finger wrote: > On 09/26/2016 06:37 AM, Rafael J. Wysocki wrote: > > On Friday, September 23, 2016 09:45:09 PM Larry Finger wrote: > >> On 09/18/2016 09:54 PM, Larry Finger wrote: > >>> On 09/14/2016 11:00 AM, Larry Finger wrote: > >>>> On 09/09/2016 12:39 PM, Larry Finger wrote: > >>>>> I have found a regression in kernel 4.8-rc2 that causes the speed of my > >>>>> laptop > >>>>> with an Intel(R) Core(TM) i7-4600M CPU @ 2.90GHz to suddenly have a > >>>>> maximum cpu > >>>>> frequency of ~400 MHz. Unfortunately, I do not know how to trigger this > >>>>> problem, > >>>>> thus a bisection is not possible. It usually happens under heavy load, > >>>>> such as a > >>>>> kernel build or the RPM build of VirtualBox, but it does not always > >>>>> fail with > >>>>> these loads. In my most recent failure, 'hwinfo --cpu' reports cpu MHz > >>>>> of > >>>>> 396.130 for #3. The bogomips value is 5787.73, and the cpu clock before > >>>>> the > >>>>> fault is 3437 MHz. Nothing is logged when this happens. > >>>>> > >>>>> If I were to get a patch that would show a backtrace when the maximum > >>>>> CPU > >>>>> frequency is changed, perhaps it would be possible to track this bug. > >>>> > >>>> I have not yet found the bad commit, but I have reduced the range of > >>>> commits a > >>>> bit. This bug has been difficult to trigger. So far, it has not taken > >>>> over 1/2 > >>>> day to appear in bad kernels, thus I am allowing three days before > >>>> deciding that > >>>> a given trial is good. I never saw the problem with 4.7 kernels, but I > >>>> did in > >>>> 4.8-rc1. I also know that it appeared before commit 581e0cd. Commit > >>>> 1b05cf6 did > >>>> not show the bug. > >>>> > >>>> Testing continues. > >>> > >>> And still does. My bisection seemed to be trending toward an improbable > >>> set of > >>> commits, and I needed to do some other work with the machine, thus I > >>> started > >>> running 4.8-rc6. It failed nearly 48 hours after the reboot, which > >>> indicated > >>> that using 3 days to indicate a "good" trial was likely too short. I am > >>> currently testing the first of the trial and will run it for at least a > >>> week. It > >>> is unlikely that these tests will be complete before 4,8 is released, > >>> even if > >>> -rc8 is needed. I will keep attempting to find the faulty commit. > >> > >> My debugging continues. After 7 days of beating on commit f7816ad, I have > >> concluded that it is likely good. Thus I think the bug lies between commit > >> 581e0cd (bad) and f7816ad (good). I will need to do a long test on commit > >> 1b05cf6, which did not fail with a shorter run. > > > > 581e0cd is not a valid mainline commit hash AFAICS. > > That was a typo. The correct value is 581e0c7. > > > > What cpufreq driver do you use? > > My "Default CPUFreq governor" is on demand. > > Running the command 'egrep -r "CPU_FREQ|CPUFREQ" .config' results in > > CONFIG_ACPI_CPU_FREQ_PSS=y > CONFIG_CPU_FREQ=y > CONFIG_CPU_FREQ_GOV_ATTR_SET=y > CONFIG_CPU_FREQ_GOV_COMMON=y > # CONFIG_CPU_FREQ_STAT is not set > # CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set > # CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE is not set > # CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE is not set > CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y > # CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE is not set > # CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL is not set > CONFIG_CPU_FREQ_GOV_PERFORMANCE=y > CONFIG_CPU_FREQ_GOV_POWERSAVE=m > CONFIG_CPU_FREQ_GOV_USERSPACE=m > CONFIG_CPU_FREQ_GOV_ONDEMAND=y > CONFIG_CPU_FREQ_GOV_CONSERVATIVE=m > # CONFIG_CPU_FREQ_GOV_SCHEDUTIL is not set > CONFIG_X86_PCC_CPUFREQ=m > CONFIG_X86_ACPI_CPUFREQ=m > CONFIG_X86_ACPI_CPUFREQ_CPB=y > > Commit 1b05cf6 did fail on longer testing, thus my bisection had ended up > going > wrong. Further tests have shown that commit 351a4ded is bad. Once again, by > bisection seems to be converging to a set of commits that seem unlikely to > cause > this problem. Perhaps commit f7816ad is not really good even though it > survived > 7 days of heavy CPU usage. > > I have been reluctant to post my entire .config on the list. It is available > at > http://pastebin.com/aMZaAKwL.
If the governor is ondemand, the driver is acpi-cpufreq, most likely. How do you measure the frequency? Thanks, Rafael
