Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH] Do not modify MSR_IA32_ENERGY_PERF_BIAS in kernel | Date | Sat, 27 Feb 2016 00:15:47 +0100 |
| |
On Friday, February 26, 2016 05:38:00 PM Thomas Renninger wrote: > The assumption that BIOSes never want to have this register being set to > full performance (zero) is wrong. > > While wrongly overruling this BIOS setting and set it from performance > to normal did not hurt that much, because nobody really knew the effects inside > Intel processors. > > But with Broadwell-EP processor (E5-2687W v4) the CPU will not enter turbo modes > if this value is not set to performance. > > So switch logic to tell the user in a friendly way (info) that the CPU is in > performance mode and how to switch via userspace if this is not intended. > > But otherwise trust that the BIOS has set the correct value here and do not > blindly overrule. > > How this has been found: SLE11 had this patch, SLE12 it slipped through. > It took quite some time to nail down that this patch missing is the reason > for not entering turbo modes with this specific processor. > > Signed-off-by: Thomas Renninger <trenn@suse.com> > > --- a/arch/x86/kernel/cpu/intel.c 2016-02-26 17:19:55.731042972 +0100 > +++ b/arch/x86/kernel/cpu/intel.c 2016-02-26 17:20:48.598020581 +0100 > @@ -377,8 +377,12 @@ static void init_intel_energy_perf(struc > u64 epb; > > /* > - * Initialize MSR_IA32_ENERGY_PERF_BIAS if not already initialized. > - * (x86_energy_perf_policy(8) is available to change it at run-time.) > + * On server platforms energy bias typically is set to > + * performance on purpose. > + * On other platforms it may happen that MSR_IA32_ENERGY_PERF_BIAS > + * did not get initialized properly by BIOS. > + * Best is to to keep BIOS settings and give the user a hint whether > + * to change it via cpupower-set(8) userspace tool at runtime. > */ > if (!cpu_has(c, X86_FEATURE_EPB)) > return; > @@ -387,10 +391,8 @@ static void init_intel_energy_perf(struc > if ((epb & 0xF) != ENERGY_PERF_BIAS_PERFORMANCE) > return; > > - pr_warn_once("ENERGY_PERF_BIAS: Set to 'normal', was 'performance'\n"); > - pr_warn_once("ENERGY_PERF_BIAS: View and update with x86_energy_perf_policy(8)\n"); > - epb = (epb & ~0xF) | ENERGY_PERF_BIAS_NORMAL; > - wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb); > + pr_info_once("ENERGY_PERF_BIAS is set to 'performance'\n"); > + pr_info_once("ENERGY_PERF_BIAS: Update with cpupower-set(8)\n");
This doesn't need to be cpupower-set IMO.
> } > > static void intel_bsp_resume(struct cpuinfo_x86 *c) >
Thanks, Rafael
| |