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MWAITX can enable a timer and a corresponding timer value specified in SW P0 clocks. The SW P0 frequency is the same as TSC. The timer provides an upper bound on how long the instruction waits before exiting. This way, a delay function in the kernel can leverage that MWAITX timer of MWAITX. When a CPU core executes MWAITX, it will be quiesced in a waiting phase, diminishing its power consumption. This way, we can save power in comparison to our default TSC-based delays. A simple test shows that: $ cat /sys/bus/pci/devices/0000\:00\:18.4/hwmon/hwmon0/power1_acc $ sleep 10000s $ cat /sys/bus/pci/devices/0000\:00\:18.4/hwmon/hwmon0/power1_acc Results: * TSC-based default delay: 485115 uWatts average power * MWAITX-based delay: 252738 uWatts average power Thus, that's about 240 milliWatts less power consumption. The test method relies on the support of AMD CPU accumulated power algorithm in fam15h_power for which patches are forthcoming. Suggested-by: Andy Lutomirski <luto@amacapital.net> Suggested-by: Borislav Petkov <bp@suse.de> Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Huang Rui <ray.huang@amd.com> [ Fix delay truncation. ] Signed-off-by: Borislav Petkov <bp@suse.de> Cc: Aaron Lu <aaron.lu@intel.com> Cc: Andreas Herrmann <herrmann.der.user@gmail.com> Cc: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Frédéric Weisbecker <fweisbec@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Hector Marco-Gisbert <hecmargi@upv.es> Cc: Jacob Shin <jacob.w.shin@gmail.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: John Stultz <john.stultz@linaro.org> Cc: Len Brown <lenb@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Rafael J. Wysocki <rjw@rjwysocki.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tony Li <tony.li@amd.com> Link: http://lkml.kernel.org/r/1438744732-1459-3-git-send-email-ray.huang@amd.com Link: http://lkml.kernel.org/r/1439201994-28067-4-git-send-email-bp@alien8.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
9 lines
169 B
C
9 lines
169 B
C
#ifndef _ASM_X86_DELAY_H
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#define _ASM_X86_DELAY_H
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#include <asm-generic/delay.h>
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void use_tsc_delay(void);
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void use_mwaitx_delay(void);
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#endif /* _ASM_X86_DELAY_H */
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