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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