From owner-freebsd-current Sat Sep 5 08:56:09 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id IAA06020 for freebsd-current-outgoing; Sat, 5 Sep 1998 08:56:09 -0700 (PDT) (envelope-from owner-freebsd-current@FreeBSD.ORG) Received: from critter.freebsd.dk (critter.freebsd.dk [212.242.40.131]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id IAA05975 for ; Sat, 5 Sep 1998 08:56:00 -0700 (PDT) (envelope-from phk@critter.freebsd.dk) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.9.1/8.8.5) with ESMTP id RAA13168; Sat, 5 Sep 1998 17:50:42 +0200 (CEST) To: Thomas Dean cc: current@FreeBSD.ORG Subject: Re: Dmesg Timecounter Varies In-reply-to: Your message of "Sat, 05 Sep 1998 08:14:15 PDT." <199809051514.IAA00899@ix.netcom.com> Date: Sat, 05 Sep 1998 17:50:42 +0200 Message-ID: <13166.905010642@critter.freebsd.dk> From: Poul-Henning Kamp Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG the "cost" is a measure of how expensive it is to get a reading from the timecounter, but it isn't used for anything (yet). The variance you see here seems abnormal, and I allthough I havn't studied the numbers statistically, I'm pretty sure I havn't seen any numbers as large as 41.6 microseconds anywhere. I have no explanation except my favourite scape-goat when it comes to lousy timekeeping: APM ? It would have been far more interesting if you had enabled the *CALIBRATE* stuff in your config and looked at the actual rates it found. In message <199809051514.IAA00899@ix.netcom.com>, Thomas Dean writes: >I have noticed that the Timecounter value varies greatly in DMESG. > >I am running an SMP kernel. I extracted the values from >/var/log/messages and passed them thru a stat process: > >Timecounter Cost Statistics >Processing /var/log/messages and /var/log/messages.?.gz > > Frequency: 1193182 Hz - Always this value, unless stated. > 1/freq Time: 838 nsec > No. Cycles: 3 - floor( mean/(1/freqTime) ). > Cycle Time: 948 nsec - mean/(no. cycles). > Overhead: 332 nsec - Total overhead in Timecounter cost. > > Entries: 125 - Number of Timecounter entries in messages. > Minimum: 2517 nsec > Maximum: 41603 nsec - Wow! Flyer! > Mean: 2846 nsec > Std. Dev.: 3494.46 > >Notice the maximum flyer. What causes this variability? > >============= dmesg ================================== > >FreeBSD 3.0-CURRENT #2: Tue Aug 18 14:05:12 PDT 1998 > root@celebris:/usr/src/sys/compile/CELEBRIS-SMP >Timecounter "i8254" frequency 1193182 Hz cost 2540 ns >CPU: Pentium/P54C (586-class CPU) > Origin = "GenuineIntel" Id = 0x525 Stepping=5 > Features=0x3bf >real memory = 100663296 (98304K bytes) >avail memory = 95268864 (93036K bytes) >FreeBSD/SMP: Multiprocessor motherboard > cpu0 (BSP): apic id: 0, version: 0x00030010, at 0xfee00000 > cpu1 (AP): apic id: 1, version: 0x00030010, at 0xfee00000 > io0 (APIC): apic id: 2, version: 0x000f0011, at 0xfec00000 >Probing for devices on PCI bus 0: >chip0: rev 0x11 on pci0.0.0 >ncr0: rev 0x02 int a irq 11 on pci0.1.0 >... >npx0 on motherboard >npx0: INT 16 interface >Intel Pentium F00F detected, installing workaround >APIC_IO: Testing 8254 interrupt delivery >APIC_IO: routing 8254 via pin 2 >changing root device to sd1s1a >SMP: AP CPU #1 Launched! > >To Unsubscribe: send mail to majordomo@FreeBSD.org >with "unsubscribe freebsd-current" in the body of the message > -- Poul-Henning Kamp FreeBSD coreteam member phk@FreeBSD.ORG "Real hackers run -current on their laptop." "ttyv0" -- What UNIX calls a $20K state-of-the-art, 3D, hi-res color terminal To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message