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Date: Thu, 31 Mar 2016 15:46:22 +0200 From: "Rafael J. Wysocki" <rjw@...ysocki.net> To: Linux PM list <linux-pm@...r.kernel.org>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com> Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: [PATCH] intel_pstate: Avoid pointless FRAC_BITS shifts under div_fp() From: Rafael J. Wysocki <rafael.j.wysocki@...el.com> There are multiple places in intel_pstate where int_tofp() is applied to both arguments of div_fp(), but this is pointless, because int_tofp() simply shifts its argument to the left by FRAC_BITS which mathematically is equivalent to multuplication by 2^FRAC_BITS, so if this is done to both arguments of a division, the extra factors will cancel each other during that operation anyway. Drop the pointless int_tofp() applied to div_fp() arguments throughout the driver. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com> --- drivers/cpufreq/intel_pstate.c | 27 +++++++++++---------------- 1 file changed, 11 insertions(+), 16 deletions(-) Index: linux-pm/drivers/cpufreq/intel_pstate.c =================================================================== --- linux-pm.orig/drivers/cpufreq/intel_pstate.c +++ linux-pm/drivers/cpufreq/intel_pstate.c @@ -206,17 +206,17 @@ static inline void pid_reset(struct _pid static inline void pid_p_gain_set(struct _pid *pid, int percent) { - pid->p_gain = div_fp(int_tofp(percent), int_tofp(100)); + pid->p_gain = div_fp(percent, 100); } static inline void pid_i_gain_set(struct _pid *pid, int percent) { - pid->i_gain = div_fp(int_tofp(percent), int_tofp(100)); + pid->i_gain = div_fp(percent, 100); } static inline void pid_d_gain_set(struct _pid *pid, int percent) { - pid->d_gain = div_fp(int_tofp(percent), int_tofp(100)); + pid->d_gain = div_fp(percent, 100); } static signed int pid_calc(struct _pid *pid, int32_t busy) @@ -394,7 +394,7 @@ static ssize_t show_turbo_pct(struct kob total = cpu->pstate.turbo_pstate - cpu->pstate.min_pstate + 1; no_turbo = cpu->pstate.max_pstate - cpu->pstate.min_pstate + 1; - turbo_fp = div_fp(int_tofp(no_turbo), int_tofp(total)); + turbo_fp = div_fp(no_turbo, total); turbo_pct = 100 - fp_toint(mul_fp(turbo_fp, int_tofp(100))); return sprintf(buf, "%u\n", turbo_pct); } @@ -465,8 +465,7 @@ static ssize_t store_max_perf_pct(struct limits->max_perf_pct); limits->max_perf_pct = max(limits->min_perf_pct, limits->max_perf_pct); - limits->max_perf = div_fp(int_tofp(limits->max_perf_pct), - int_tofp(100)); + limits->max_perf = div_fp(limits->max_perf_pct, 100); if (hwp_active) intel_pstate_hwp_set_online_cpus(); @@ -490,8 +489,7 @@ static ssize_t store_min_perf_pct(struct limits->min_perf_pct); limits->min_perf_pct = min(limits->max_perf_pct, limits->min_perf_pct); - limits->min_perf = div_fp(int_tofp(limits->min_perf_pct), - int_tofp(100)); + limits->min_perf = div_fp(limits->min_perf_pct, 100); if (hwp_active) intel_pstate_hwp_set_online_cpus(); @@ -973,8 +971,8 @@ static inline int32_t get_target_pstate_ * specified pstate. */ core_busy = cpu->sample.core_pct_busy; - max_pstate = int_tofp(cpu->pstate.max_pstate_physical); - current_pstate = int_tofp(cpu->pstate.current_pstate); + max_pstate = cpu->pstate.max_pstate_physical; + current_pstate = cpu->pstate.current_pstate; core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate)); /* @@ -986,8 +984,7 @@ static inline int32_t get_target_pstate_ duration_ns = cpu->sample.time - cpu->last_sample_time; if ((s64)duration_ns > pid_params.sample_rate_ns * 3 && cpu->last_sample_time > 0) { - sample_ratio = div_fp(int_tofp(pid_params.sample_rate_ns), - int_tofp(duration_ns)); + sample_ratio = div_fp(pid_params.sample_rate_ns, duration_ns); core_busy = mul_fp(core_busy, sample_ratio); } @@ -1167,10 +1164,8 @@ static int intel_pstate_set_policy(struc /* Make sure min_perf_pct <= max_perf_pct */ limits->min_perf_pct = min(limits->max_perf_pct, limits->min_perf_pct); - limits->min_perf = div_fp(int_tofp(limits->min_perf_pct), - int_tofp(100)); - limits->max_perf = div_fp(int_tofp(limits->max_perf_pct), - int_tofp(100)); + limits->min_perf = div_fp(limits->min_perf_pct, 100); + limits->max_perf = div_fp(limits->max_perf_pct, 100); out: intel_pstate_set_update_util_hook(policy->cpu);
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