Date: Wed, 24 Sep 2008 00:17:18 +0400 From: Ruslan Ermilov <ru@FreeBSD.org> To: gnn@freebsd.org Cc: net@freebsd.org Subject: Re: Proposed patch, convert IFQ_MAXLEN to kernel tunable... Message-ID: <20080923201718.GA88008@edoofus.dev.vega.ru> In-Reply-To: <m2skrq7jb1.wl%gnn@neville-neil.com> References: <m2skrq7jb1.wl%gnn@neville-neil.com>
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Hi, On Tue, Sep 23, 2008 at 03:29:06PM -0400, gnn@freebsd.org wrote: > It turns out that the last time anyone looked at this constant was > before 1994 and it's very likely time to turn it into a kernel > tunable. On hosts that have a high rate of packet transmission > packets can be dropped at the interface queue because this value is > too small. Rather than make a sweeping code change I propose the > following change to the macro and updating a couple of places in the > IP and IPv6 stacks that were using this macro to set their own global > variables. > > I have tested this in my test lab at work, it is not as yet in > production at my day job, but will be soon. > It's not that bad -- most modern Ethernet drivers initialize interface input queues themselves, and don't depend on IFQ_MAXLEN. The IPv4 input queue is tunable via net.inet.ip.intr_queue_maxlen. The IPv6 queue can similarly be made tunable. I agree that ifqmaxlen can be made tunable because there's still a lot of (mostly for old hardware) drivers that use ifqmaxlen and IFQ_MAXLEN, but I'm against changing the definition of IFQ_MAXLEN. Imagine some code like this: void *x[IFQ_MAXLEN]; // here it's 50 And some function that does: for (i = 0; i < IFQ_MAXLEN; i++) { // not necessarily 50 x[i] = NULL; } Cheers, -- Ruslan Ermilov ru@FreeBSD.org FreeBSD committer
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