* Len Brown <lenb@xxxxxxxxxx> wrote: > > > > From: Len Brown <len.brown@xxxxxxxxx> > > > > > > Since 2.6.35 (23016bf0d25), Linux prints the existence of "epb" in /proc/cpuinfo, > > > Since 2.6.38 (d5532ee7b40), the x86_energy_perf_policy(8) utility is available > > > in-tree to update MSR_IA32_ENERGY_PERF_BIAS. > > > > > > However, the typical BIOS fails to initialize the MSR, > > > and the typical Linux distro neglects to invoke x86_energy_perf_policy(8). > > > > > > The result is that some modern hardware is running in hardware default, > > > which is "performance" mode, rather than the intended design default > > > of "normal" mode. > > > > > > Initialize the MSR to the "normal" setting during kernel boot. > > > > > > Of course, x86_energy_perf_policy(8) is available to change > > > the default after boot, should the user have a policy preference. > > > > > > cc: stable@xxxxxxxxxx > > > Signed-off-by: Len Brown <len.brown@xxxxxxxxx> > > > --- > > > arch/x86/include/asm/msr-index.h | 3 +++ > > > arch/x86/kernel/cpu/intel.c | 14 ++++++++++++++ > > > 2 files changed, 17 insertions(+), 0 deletions(-) > > > > ... > > > > Dunno, this patch appears to silently modify the system to be slower than it > > was before under Linux. > > > > Won't people report this as a regression if this change reduces performance for > > them? > > > > They wont be able to see your comments in the code and in the changelog either, > > when this happens to them. They might look into /proc/cpuinfo and see 'epb' > > there but it wont tell them anything. They wont know about a utility available > > in tools/power/x86/ either. > > This patch makes no change to the epb feature indicator > /proc/cpuinfo. I know. I reacted to this bit in the changelog: > > > Since 2.6.35 (23016bf0d25), Linux prints the existence of "epb" in /proc/cpuinfo, Printing the existence of a CPU feature does nothing to inform users. > > So this patch has 'future trouble' written all over it i'm afraid. > > EPB is limited to SNB and later. > So the installed base as yet is small. > (it also exists on WSM-EP, but doesn't do so much there) > EPB will have a more significant effect on future hardware. > > Linux currently trails competing operating systems in energy > efficiency on SNB due to this setting, and Linux will trail > competing operating systems even more on future hardware > if this default is not fixed. > > Will it be possible to measure a performance difference between > "performance" and "normal"? Yes, it will be possible. > Will 99.9% of users notice? Nope. More likely they'll notice > the the power savings that are disabled in "performance" mode. > > I should have called it "benchmark" mode instead of "performance" mode... That's all fair but does not address the concerns i raised. A silent change during bootup is asking for trouble. So how about informing users, how about making it non-silent? An informative printk that also mentions the power configuration tool, etc. This solves the concerns i mentioned. Thanks, Ingo _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
