Date: Tue, 23 Sep 2008 23:35:57 -0400 From: gnn@FreeBSD.org To: Ruslan Ermilov <ru@FreeBSD.org> Cc: net@FreeBSD.org Subject: Re: Proposed patch, convert IFQ_MAXLEN to kernel tunable... Message-ID: <m2ej3a6wrm.wl%gnn@neville-neil.com> In-Reply-To: <20080923201718.GA88008@edoofus.dev.vega.ru> References: <m2skrq7jb1.wl%gnn@neville-neil.com> <20080923201718.GA88008@edoofus.dev.vega.ru>
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At Wed, 24 Sep 2008 00:17:18 +0400,
Ruslan Ermilov wrote:
>
> 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:
>
Sorry, this is about the output queue, not the input queue.
Though there are both input and output queues that depend on 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;
> }
>
I found no occurrences of the above in our code base. I used cscope
to search all of src/sys. Are you aware of any occurrences of this?
Best,
George
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