Date: Thu, 07 Jun 2012 11:38:29 +0300 From: Alexander Motin <mav@FreeBSD.org> To: Andriy Gapon <avg@FreeBSD.org> Cc: freebsd-stable@FreeBSD.org, freebsd-acpi@FreeBSD.org, sbruno@FreeBSD.org, Yamagi Burmeister <lists@yamagi.org>, seanbru@yahoo-inc.com, Jung-uk Kim <jkim@FreeBSD.org> Subject: Re: [stable 9] broken hwpstate calls Message-ID: <4FD06885.4050507@FreeBSD.org> In-Reply-To: <4FD061F8.6030905@FreeBSD.org> References: <1337319129.2915.4.camel@powernoodle-l7> <4FB6765A.2050307@FreeBSD.org> <1337710214.2916.8.camel@powernoodle-l7.corp.yahoo.com> <20120525163653.b61a08e2.lists@yamagi.org> <4FBFA9A9.7020806@FreeBSD.org> <4FBFBD39.7000105@FreeBSD.org> <4FBFDFFB.9020501@FreeBSD.org> <4FBFE624.1020208@FreeBSD.org> <20120526090233.f638c1d2.lists@yamagi.org> <4FC0A3A1.80200@FreeBSD.org> <4FC7D464.20602@FreeBSD.org> <4FCFD2A1.60706@FreeBSD.org> <4FCFE178.9080505@FreeBSD.org> <4FD061F8.6030905@FreeBSD.org>
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On 06/07/12 11:10, Andriy Gapon wrote: > on 07/06/2012 02:02 Jung-uk Kim said the following: >> Any way, hwpstate still isn't quite right even without your patch. >> >> sys/kern/kern_cpu.c cpufreq_curr_sysctl() -> CPUFREQ_SET() -> /* for all >> CPU devices */ cf_set_method() -> /* thread_lock(), sched_bind(), ... */ >> CPUFREQ_DRV_SET() -> sys/x86/cpufreq/hwpstate.c hwpstate_set() -> >> hwpstate_goto_pstate() /* for each CPU unit */ /* thread_lock(), >> sched_bind(), ... */ > > Oh, I didn't realize that there was the cpufreq-level loop over all CPUs! > That really sucks. > > Maybe some day we should accept that different CPUs could legitimately be in > different P-states and provide support for that throughout the stack (from > powerd to drivers). Support for different P-states on different CPUs can be useful if CPUs have different capabilities. I believe it is very rare, but possible. At this moment cpufreq should set for each CPU frequency closest to one that was set on BSP. It should be possible to make powerd to read sets of frequencies from all CPUs and do the same, just more intelligently. Same time using very different frequencies for different CPUs can IMHO be very problematic even in theory. For SMP systems it is quite difficult (because of threads migration and possible inter-operations of multiple threads) to identify cases when even global frequency can be reduced without proportional performance penalty. Making in per-CPU multiplies number of options and requires awareness from the scheduler. -- Alexander Motin
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