Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932476AbaFKOIc (ORCPT ); Wed, 11 Jun 2014 10:08:32 -0400 Received: from sema.semaphore.gr ([78.46.194.137]:60034 "EHLO sema.semaphore.gr" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1753971AbaFKOIb (ORCPT ); Wed, 11 Jun 2014 10:08:31 -0400 Message-ID: <539862DB.9060905@semaphore.gr> Date: Wed, 11 Jun 2014 17:08:27 +0300 From: Stratos Karafotis User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Doug Smythies , rjw@rjwysocki.net, viresh.kumar@linaro.org, dirk.j.brandewie@intel.com CC: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] cpufreq: intel_pstate: Fix rounding of core_pct References: <1402490012-19969-1-git-send-email-stratosk@semaphore.gr> <009b01cf857a$d5032090$7f0961b0$@net> In-Reply-To: <009b01cf857a$d5032090$7f0961b0$@net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/06/2014 04:41 μμ, Doug Smythies wrote: > > On 2014.06.11 05:34 Stratos Karafotis wrote: > >> Local variable core_pct holds fixed point values. >> When we round it we add "1" to core_pct. This has almost >> no effect. >> >> So, add int_toftp(1) to core_pct when rounding. >> >> For example, in a given sample point (values taken from >> tracepoint) with: >> aperf = 5024 >> mperf = 10619 >> >> the core_pct is (before rounding): >> core_pct = 12111 >> fp_toint(core_pct) = 47 >> >> After rounding: >> core_pct = 12112 >> fp_toint(core_pct) = 47 >> >> After rounding with int_toftp(1): >> core_pct = 12367 >> fp_toint(core_pct) = 48 >> >> Signed-off-by: Stratos Karafotis >> --- >> >> Hi Rafael, >> >> I'm sorry for submitting again in merge window, but >> I thought that maybe we need this fix for 3.16. >> >> >> drivers/cpufreq/intel_pstate.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c >> index 4e7f492..dd80aa2 100644 >> --- a/drivers/cpufreq/intel_pstate.c >> +++ b/drivers/cpufreq/intel_pstate.c >> @@ -564,7 +564,7 @@ static inline void intel_pstate_calc_busy(struct cpudata *cpu) >> core_pct = div_u64_rem(core_pct, int_tofp(sample->mperf), &rem); >> >> if ((rem << 1) >= int_tofp(sample->mperf)) >> - core_pct += 1; >> + core_pct += int_tofp(1); >> >> sample->freq = fp_toint( >> mul_fp(int_tofp(cpu->pstate.max_pstate * 1000), core_pct)); >> -- >> 1.9.3 > > No. > > The intent was only ever to round properly the pseudo floating point result of the divide. > It was much more important (ugh, well 4 times more) when FRACBITS was still 6, which also got changed to 8 in a recent patch. > Are you sure? This rounding was very recently added. As far as I can understand, I don't see the meaning of this rounding, as is. Even if FRAC_BITS was 6, I think it would have almost no improvement in calculations. Stratos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/