ACPI: create "processor.bm_check_disable" boot param
in [Kernel]
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From: Andi Kleen on 26 Jul 2010 03:30 Len Brown <lenb(a)kernel.org> writes: > > Note also that an alternative for newer systems > is to use the intel_idle driver, which always > ignores BM_STS, relying Linux device drivers > to register constraints explicitly via PM_QOS. > > https://bugzilla.kernel.org/show_bug.cgi?id=15886 Thanks. I don't fully understand why the check for this option is in a different place than the register check in the earlier patch? This needs to be also documented in Documentation/kernel-parameters.txt Other than that it looks good. -Andi -- ak(a)linux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Len Brown on 26 Jul 2010 20:30 > > Note also that an alternative for newer systems > > is to use the intel_idle driver, which always > > ignores BM_STS, relying Linux device drivers > > to register constraints explicitly via PM_QOS. > > > > https://bugzilla.kernel.org/show_bug.cgi?id=15886 > > Thanks. I don't fully understand why the check for this option > is in a different place than the register check in the earlier patch? Technically, it could have been. There are a comple of constraints in the layout of this code. The _CST flag is x86 (actually Intel) specific -- so the detection went into arch/x86/kernel/acpi/cstate.c However, the operation of the that flag is per C-state, not necessarily per system -- so we remember the flag in in a cx->bm_sts_skip flag and check it in the 'acpi generic' drivers/acpi/processor_idle.c But we can't test a per cx flag inside acpi_idle_bm_check() because it doesn't have access to the cx, so i put that test at the site of its only caller. In this 2nd patch... we added a 'generic' ACPI bootparam that applies to all C-states. So it overrides any per-cstate flag and it is static to the processor_idle.c file, so it seemed cleanest (to me) to push it down inside acpi_idle_bm_check() rather than in its only caller. > This needs to be also documented in Documentation/kernel-parameters.txt I thought about that and decided against it. While we do document some driver specific modparams in kernel-parameters.txt, I do not expect this one to be used that often -- mostly for diagnosis of BIOS bugs. I know of two machines that need it, and both of those machines have a BIOS update or a BIOS update in progress that make it unnecessary. thanks for caring. Len Brown, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Andi Kleen on 28 Jul 2010 10:20 > > This needs to be also documented in Documentation/kernel-parameters.txt > > I thought about that and decided against it. > While we do document some driver specific modparams > in kernel-parameters.txt, I do not expect this one to > be used that often -- mostly for diagnosis of BIOS bugs. > I know of two machines that need it, > and both of those machines have a BIOS update > or a BIOS update in progress that make it unnecessary. I think even obscure parameters should be documented. -Andi -- ak(a)linux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Len Brown on 28 Jul 2010 15:00 On Tue, 27 Jul 2010, Andi Kleen wrote: > > > This needs to be also documented in Documentation/kernel-parameters.txt > > > > I thought about that and decided against it. > > While we do document some driver specific modparams > > in kernel-parameters.txt, I do not expect this one to > > be used that often -- mostly for diagnosis of BIOS bugs. > > I know of two machines that need it, > > and both of those machines have a BIOS update > > or a BIOS update in progress that make it unnecessary. > > I think even obscure parameters should be documented. Where? kernel-parameters.txt seems to be mostly about core kernel parameters. While there are some key driver parameters in there, they appear to be the exception. -Len -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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