Date: Tue, 2 Oct 2007 14:43:38 -0400 From: John Baldwin <jhb@freebsd.org> To: Bruce Evans <brde@optusnet.com.au> Cc: src-committers@freebsd.org, cvs-src@freebsd.org, Jeff Roberson <jeff@freebsd.org>, Garance A Drosehn <gad@freebsd.org>, Ben Kaduk <minimarmot@gmail.com>, cvs-all@freebsd.org, Jeff Roberson <jroberson@chesapeake.net> Subject: Re: cvs commit: src/sys/kern sched_ule.c Message-ID: <200710021443.40264.jhb@freebsd.org> In-Reply-To: <20071002213829.F12287@delplex.bde.org> References: <20071001145257.EC9FC4500F@ptavv.es.net> <20071001232743.Q539@10.0.0.1> <20071002213829.F12287@delplex.bde.org>
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On Tuesday 02 October 2007 09:49:34 am Bruce Evans wrote: > Apparently, there is a scaling bug for hz or extra interrupts for > the larger hz help, and the default preempt_thresh is not best. -current on i386 and amd64 does a very poor job of scaling stathz and profhz with hz, so this may explain problems at hz=100. I have an attempt to make stathz and profhz more sane while also trying to not always drive the lapic timer at hz * 2. I used to have a test program that would display all the frequencies for different 'hz' values but have misplaced it. :( --- //depot/vendor/freebsd/src/sys/amd64/amd64/local_apic.c 2007/09/11 22:57:37 +++ //depot/user/jhb/acpipci/amd64/amd64/local_apic.c 2007/09/24 17:24:13 @@ -72,8 +72,6 @@ CTASSERT(IPI_STOP < APIC_SPURIOUS_INT); #define LAPIC_TIMER_HZ_DIVIDER 2 -#define LAPIC_TIMER_STATHZ_DIVIDER 15 -#define LAPIC_TIMER_PROFHZ_DIVIDER 3 /* Magic IRQ values for the timer and syscalls. */ #define IRQ_TIMER (NUM_IO_INTS + 1) @@ -383,13 +381,24 @@ lapic_timer_divisor, value); /* - * We will drive the timer at a small multiple of hz and drive - * both of the other timers with similarly small but relatively - * prime divisors. + * We want to run stathz in the neighborhood of 128hz. We would + * like profhz to run as often as possible, so we let it run on + * each clock tick. We try to honor the requested 'hz' value as + * much as possible. + * + * If 'hz' is above 1500, then we just let the lapic timer + * (and profhz) run at hz. If 'hz' is below 1500 but above + * 750, then we let the lapic timer run at 2 * 'hz'. If 'hz' + * is below 750 then we let the lapic timer run at 4 * 'hz'. */ - lapic_timer_hz = hz * LAPIC_TIMER_HZ_DIVIDER; - stathz = lapic_timer_hz / LAPIC_TIMER_STATHZ_DIVIDER; - profhz = lapic_timer_hz / LAPIC_TIMER_PROFHZ_DIVIDER; + if (hz >= 1500) + lapic_timer_hz = hz; + else if (hz >= 750) + lapic_timer_hz = hz * 2; + else + lapic_timer_hz = hz * 4; + stathz = lapic_timer_hz / (lapic_timer_hz * 128); + profhz = lapic_timer_hz; lapic_timer_period = value / lapic_timer_hz; /* --- //depot/vendor/freebsd/src/sys/i386/i386/local_apic.c 2007/09/11 22:57:37 +++ //depot/user/jhb/acpipci/i386/i386/local_apic.c 2007/09/24 17:24:13 @@ -72,8 +72,6 @@ CTASSERT(IPI_STOP < APIC_SPURIOUS_INT); #define LAPIC_TIMER_HZ_DIVIDER 2 -#define LAPIC_TIMER_STATHZ_DIVIDER 15 -#define LAPIC_TIMER_PROFHZ_DIVIDER 3 /* Magic IRQ values for the timer and syscalls. */ #define IRQ_TIMER (NUM_IO_INTS + 1) @@ -385,13 +383,24 @@ lapic_timer_divisor, value); /* - * We will drive the timer at a small multiple of hz and drive - * both of the other timers with similarly small but relatively - * prime divisors. + * We want to run stathz in the neighborhood of 128hz. We would + * like profhz to run as often as possible, so we let it run on + * each clock tick. We try to honor the requested 'hz' value as + * much as possible. + * + * If 'hz' is above 1500, then we just let the lapic timer + * (and profhz) run at hz. If 'hz' is below 1500 but above + * 750, then we let the lapic timer run at 2 * 'hz'. If 'hz' + * is below 750 then we let the lapic timer run at 4 * 'hz'. */ - lapic_timer_hz = hz * LAPIC_TIMER_HZ_DIVIDER; - stathz = lapic_timer_hz / LAPIC_TIMER_STATHZ_DIVIDER; - profhz = lapic_timer_hz / LAPIC_TIMER_PROFHZ_DIVIDER; + if (hz >= 1500) + lapic_timer_hz = hz; + else if (hz >= 750) + lapic_timer_hz = hz * 2; + else + lapic_timer_hz = hz * 4; + stathz = lapic_timer_hz / (lapic_timer_hz * 128); + profhz = lapic_timer_hz; lapic_timer_period = value / lapic_timer_hz; /* -- John Baldwin
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