Re: [net-next-2.6 PATCH v5 2/2] net_sched: implement a root container qdisc sch_mqprio

On Wed, Jan 05, 2011 at 06:31:09PM -0800, John Fastabend wrote:

On 1/5/2011 4:32 PM, Jarek Poplawski wrote:

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On Wed, Jan 05, 2011 at 09:38:44AM -0800, John Fastabend wrote:

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On 1/4/2011 2:59 PM, Jarek Poplawski wrote:

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On Tue, Jan 04, 2011 at 10:56:46AM -0800, John Fastabend wrote:

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+
+     /* Always use supplied priority mappings */
+     for (i = 0; i < TC_BITMASK + 1; i++) {
+             if (netdev_set_prio_tc_map(dev, i, qopt->prio_tc_map[i])) {
+                     err = -EINVAL;

This would probably trigger if we try qopt->num_tc == 0. Is it expected?

netdev_set_prio_tc_map() returns 0 on sucess. This if(..) is a bit strange though.

        err = netdev_set_prio_tc_map(dev, i, qopt->prio_tc_map[i])
        if (err)
                ...

Is cleaner IMHO.

Maybe. But I still wonder if qopt->num_tc == 0 is valid (by design)?
(netdev_set_prio_tc_map() returns -EINVAL if dev->num_tc == 0)

I guess I don't see how it returns -EINVAL. Although setting
qopt->num_tc = 0 is equivalent to disabling traffic classes so
it is a strange thing to do but I don't expect it should be a
problem.

static inline
int netdev_set_prio_tc_map(struct net_device *dev, u8 prio, u8 tc)
{
        if (tc >= dev->num_tc)

If dev->num_tc was set to 0 this check is always true and we exit
the init with error. It's not a problem if it's documented but
checking it earlier seems more readable.

                return -EINVAL;

        dev->prio_tc_map[prio & TC_BITMASK] = tc & TC_BITMASK;
        return 0;
}

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+static unsigned long mqprio_get(struct Qdisc *sch, u32 classid)
+{
+     unsigned int ntx = TC_H_MIN(classid);

We need to 'get' tc classes too, eg for individual dumps. Then we
should omit them in .leaf, .graft etc.

OK missed this. Looks like iproute2 always sets NLM_F_DUMP which works because it uses cl_ops->walk

# tc -s class show dev eth3 classid 800b:1
class mqprio 800b:1 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0

OK, then it might be only of theoretical value (for some other tools).

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Why dev->num_tc above, netdev_get_num_tc(dev) here, and dev->num_tc
below?

No reason just inconsistant I will use dev->num_tc.

Well, this would suggest netdev_get_num_tc() is redundant.

Guess it is I can remove it.

If you definitely don't expect any #ifdef CONFIG_XXX for this code,
both get and set num_tc could be removed. If you're not sure use the
function everywhere.

static inline
u8 netdev_get_num_tc(const struct net_device *dev)
{
        return dev->num_tc;
}

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+static void mqprio_walk(struct Qdisc *sch, struct qdisc_walker *arg)
+{
+     struct net_device *dev = qdisc_dev(sch);
+     unsigned long ntx;
+     u8 num_tc = netdev_get_num_tc(dev);
+
+     if (arg->stop)
+             return;
+
+     /* Walk hierarchy with a virtual class per tc */
+     arg->count = arg->skip;
+     for (ntx = arg->skip; ntx < dev->num_tx_queues + num_tc; ntx++) {

Should we report possibly unused/unconfigured tx_queues?

I think it may be OK select_queue() could push skbs onto these queues and we may still want to see the statistics in this case. Although (real_num_tx_queues + num_tc) may make sense I see no reason to show queues above real_num_tx_queues.

IMHO, pushing skbs to unconfigured/unwanted/disabled queues is a bug,
and select should handle this, but probably it's a matter of taste.

certainly a bug for queues >= real_num_tx_queues.

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Btw, I wonder how dev->real_num_tx_queues is obeyed here.

Its not. real_num_tx_queues is not handled correctly here also
real_num_tx_queues can be changed so this need to be handled as well.
This means an additional check in the options parsing.

Well, let's do it. Maybe similarly to sch_multiq, with the .change
option?

Jarek P.