Date: Sun, 16 Jul 2000 18:09:31 +1000 From: Stephen McKay <mckay@thehub.com.au> To: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> Cc: mckay@thehub.com.au (Stephen McKay), freebsd-current@FreeBSD.ORG Subject: Re: dc driver and underruns (was: Strangeness with 4.0-S) Message-ID: <200007160809.SAA21950@dungeon.home> In-Reply-To: <200007150016.RAA18115@gndrsh.dnsmgr.net> from "Rodney W. Grimes" at "Fri, 14 Jul 2000 17:16:49 -0700" References: <200007150016.RAA18115@gndrsh.dnsmgr.net>
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On Friday, 14th July 2000, "Rodney W. Grimes" wrote: >> I suspect an interaction between the ATA driver and VIA chipsets, >> because other than the network, that's all that is operating when I see >> the underruns. And my Celeron with a ZX chipset is immune. > >I've seen them on just about everything, chipset doesn't seem to matter, >IDE or SCSI doesn't seem to matter. Well, maybe they are just a fact of life. But using just my vague knowledge of how PCI works, it doesn't look inevitable to me. So I see bugs. :-) >> Getting even more technical, it appears to me that the current driver >> instructs the 21143 to poll for transmit packets (ie a small DMA) >> every 80us even if there are none to be sent. I don't know what percentage >> of bus time this might be, or even how to calculate it (got some time Rod?) > >I'll have to look at that. If it is a simple 32 bit read every 80uS >thats something like .1515% of the PCI bandwidth, something that shouldn't >matter much. (I assumed a simple 4 cycle PCI operation). Just how big >is this DMA operation every 80uS? I believe it is just one 32 bit read. But I don't understand that aspect of the hardware very well yet. I also suspect that this polling adds to the latency, but again, I haven't got to the end of that either. Sometimes other things can distract you from even the most interesting technical matter. :-) Stephen. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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