Date: Fri, 17 Nov 2000 11:24:00 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: John Hay <jhay@icomtek.csir.co.za> Cc: mark@grondar.za, arch@FreeBSD.org Subject: Re: new monotime() call for all architectures. Message-ID: <XFMail.001117112400.jhb@FreeBSD.org> In-Reply-To: <200011171909.eAHJ9et99988@zibbi.icomtek.csir.co.za>
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On 17-Nov-00 John Hay wrote: >> >> I need a fast-as-possible "time" inside the kernel to help >> >> speed up the /dev/random device. I say "time", because although >> >> it needs to be a function of time (preferably accurate and linear), >> >> it has no need whatsoever to be "real time", so a simple counter >> >> is quite OK. >> >> >> >> Pentiums, Alphas and IA64's all have a suitable register on chip, >> >> while I have to make do with nanotime(9) on i386 and i486. >> >> >> >> I have prepared a monotime(9) call for the i386, alpha and ia64 >> >> architectures (patch enclosed). I have been running this for a >> >> week or two now with promising results (on a Pentium). With >> >> the exception of the minimum of "glue" (and nanotime on older >> >> architectures), these functions reduce to one instruction. >> >> >> > >> > Are you sure it will work on SMP machines? There is nothing that >> > synchronizes the onboard counters. Or will your code stay on one >> > cpu? >> >> It doesn't matter. He just needs a psuedo-timestamp for entropy gathering >> purposes. It dosen't need to be entirely precise, so if different CPU's >> counters are not 100% in sync it won't hurt anything. > > Ok, I just thought the "mono" in his function name is for monotonic. If > you are staying on one processor it will work, but if the timestamps > have scheduling inbetween the timestamps and you land on a different > processor it won't be monotonic anymore. It's close enough. :) > John -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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