Messages in this thread | | | Subject | Re: [BISECTED]: Kernel panic (was: Linux 5.7-rc2) | From | Giovanni Gherdovich <> | Date | Wed, 22 Apr 2020 13:01:24 +0200 |
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On Wed, 2020-04-22 at 12:22 +0200, Harald Arnesen wrote: > Harald Arnesen [22.04.2020 11:37]: > > > Giovanni Gherdovich [22.04.2020 11:02]: > > > > > > Harald: > > > > > > I'll echo Linus' request of testing that the patch series linked above fixes > > > the problem on your machine. Since you're testing -rc kernels and bisecting > > > bugs I assume you're comfortable with patching and compiling kernels, but if > > > that is not the case I am more than happy to assist by providing either an RPM > > > or a DEB package, depending on the distribution you're running. Let me know. > > Will try patching first, if I'm not successful, you may compile a DEB > > package for me. > > I can confirm that my Thinkpad T510i boots normally with the four > patches added. > > Thanks!
That's awesome, thank you for testing.
Regarding the turbostat output you attached to an earlier email, it confirms the suspicion that the 4C turbo is reported as zero (being a 2 cores / 4 threads machine), explaining why the fix works:
cpu2: MSR_TURBO_RATIO_LIMIT: 0x00001313 19 * 133.3 = 2533.3 MHz max turbo 2 active cores 19 * 133.3 = 2533.3 MHz max turbo 1 active cores
In the above, bits 31:24 are zero. It's not a universal rule, though: my laptop also has a 2 cores / 4 threads cpu, and that same MSR says:
cpu3: MSR_TURBO_RATIO_LIMIT: 0x1b1b1b1b1b1d 27 * 100.0 = 2700.0 MHz max turbo 6 active cores 27 * 100.0 = 2700.0 MHz max turbo 5 active cores 27 * 100.0 = 2700.0 MHz max turbo 4 active cores 27 * 100.0 = 2700.0 MHz max turbo 3 active cores 27 * 100.0 = 2700.0 MHz max turbo 2 active cores 29 * 100.0 = 2900.0 MHz max turbo 1 active cores
So despite my CPU being similar to yours, it wouldn't show the bug. There is even more: the bug can show on large core counts too, as seen in https://lore.kernel.org/lkml/bf43772d-48e5-01d4-dd03-330110e487fa@linux.intel.com/ Like Xu from Intel has an Atom P-Series with 24 physical cores, yet their MSR goes like:
MSR_TURBO_RATIO_LIMIT: 0x00000016
which means only the 1C turbo is reported non-zero (that machine doesn't have turbo at all, 1C turbo is the same as base frequency).
Thanks, Giovanni
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