Date: Sat, 05 Sep 1998 00:41:31 -0700 From: Mike Smith <mike@smith.net.au> To: Bill Paul <wpaul@skynet.ctr.columbia.edu> Cc: hackers@FreeBSD.ORG Subject: Re: Questions for networking gurus Message-ID: <199809050741.AAA02105@dingo.cdrom.com> In-Reply-To: Your message of "Fri, 04 Sep 1998 19:26:53 EDT." <199809042326.TAA13218@skynet.ctr.columbia.edu>
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[... describes ethernet hardware designed by idiots, and possible workaround ...] > 2) What's the longtest time than an mbuf chain with received packet data > will survive inside the kernel? The driver has to allocate enough > memory so that it can continue handling data from the chip while > waiting for previous buffers to be freed by the protocols, but if > an mbuf can get hung up inside the protocols for a very long time > (or worse, be locked indefinitely), then the buffer allocation > would be ridiculously large. This would outweight the benefit of > avoiding copies. I would have to worry about an mbuf that gets routed into the outbound queue for a slow (eg. ppp) interface. I'd expect that such a sucker would lie around for far longer than you might want. > So, does this scheme sound sensible or should I just swallow my pride > and settle for using m_devget(). It would be nice to find a way to > actually squeeze some decent performance out of this gawdawful device > just to spite the designers. If anybody has tried to do something like > this before, or is familiar with the guts of the BSD networking code, > I'd appreciate any insights. I think that their rationalisation for using busmaster DMA was simply to avoid the need for SRAM on the card, thus lowering manufacturing costs. I fear that pride-swallowing may be in order. 8( -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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