Date: Wed, 22 Nov 2000 02:59:59 +0900 From: Kenjiro Cho <kjc@csl.sony.co.jp> To: julian@elischer.org Cc: net@freebsd.org Subject: Re: ALTQ as standard..... Message-ID: <20001122025959Z.kjc@csl.sony.co.jp> In-Reply-To: <3A1A74D4.CF5AEF4F@elischer.org> References: <3A1A74D4.CF5AEF4F@elischer.org>
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ALTQ can be viewed as (1) abstraction of the output queue and (2) an implementation based on (1) I'd like to focus on (1) for our discussion for the moment. The output queue is the place where packet scheduling and buffer management can be done. The current IF macros are incomplete (e.g., lack of a poll operation), and its model lacks enough abstraction to accommodate algorithms other than FIFO. I'm trying to make the output queue as a black-box with a set of well-defined operations, and modify the existing code to access the output queue only through these operations. Although we have to first convert the existing drivers to use these operations, I believe it will pay off in the long run. Once we have a clean model of the output queue, modifications to the internal structure do not affect the other part of the kernel, be it ALTQ or another implementation. (this approach is also preferable for SMP.) In ALTQ, the following 4 operations are used. - ENQUEUE enqueues a packet to the queue. ENQUEUE also takes care of packet dropping. if the arriving packet is dropped, the mbuf is freed and an error (ENOBUFS) is returned. - DEQUEUE dequeues a packet from the queue. - POLL returns the next packet without removing the packet from the queue. if DEQUEUE immediately follows POLL, the same packet is returned. (locking will be needed for SMP.) - PURGE discards all the packets in the queue. (this operation is needed for non-work conserving schedulers which cannot get emptied by a dequeue-loop.) In this model, a driver can poll-and-dequeue a packet but cannot prepend a packet back to the queue because it could be too expensive for some algorithms to cancel scheduling once the internal state is updated. Thus, if a driver currently use "prepend-if-failed", it should be converted to "poll-and-dequeue". I'll write a brief design note in a week (so that I can submit it to Freenix). I'll post it to the list when I'm done. -Kenjiro To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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