Date: Tue, 12 Jan 1999 08:32:38 +1100 From: Peter Jeremy <peter.jeremy@auss2.alcatel.com.au> To: steve@Watt.COM Cc: freebsd-stable@FreeBSD.ORG Subject: Re: IRQ entropy causes panics? Message-ID: <99Jan12.083159est.40333@border.alcanet.com.au>
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On Sat 9th January, Steve Watt <steve@Watt.COM> wrote: >Is there a microtime() call already made at each interrupt entry? No. > Something on >the order of 5uS on a faster ISA system I tested on On a non-SMP P5 or later system RDTSC is a cheap and accurate alternative. [The problem on SMP systems is that the TSCs aren't synchronised so you need to know which CPU you are on to use it]. On 3.x, both microtime() and nanotime() will use RDTSC (and not perform any ISA bus cycles) if a working TSC is found, SMP is not defined and either it isn't an APM BIOS, or APM isn't compiled into the kernel. The actual clock being used, together with the lowest level overhead of calling it, is reported by default during boot, eg 'Timecounter "i8254" frequency 1193182 Hz cost 2376 ns' On 2.x, microtime() will use RDTSC if support for 586/686 is compiled in and a working TSC is found. Peter -- Peter Jeremy (VK2PJ) peter.jeremy@alcatel.com.au Alcatel Australia Limited 41 Mandible St Phone: +61 2 9690 5019 ALEXANDRIA NSW 2015 Fax: +61 2 9690 5982 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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