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Date: Wed, 18 Mar 2015 17:21:08 +0100
From: Imre Palik <imrep.amz@...il.com>
To: Wei Liu <wei.liu2@...rix.com>
CC: Ian Campbell <ian.campbell@...rix.com>,
xen-devel@...ts.xenproject.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, "Palik, Imre" <imrep@...zon.de>,
Anthony Liguori <aliguori@...zon.com>
Subject: Re: [RFC PATCH] xen-netback: making the bandwidth limiter runtime
settable
On 03/17/15 12:17, Wei Liu wrote:
> On Fri, Mar 13, 2015 at 01:51:05PM +0100, Imre Palik wrote:
>> From: "Palik, Imre" <imrep@...zon.de>
>>
>> With the current netback, the bandwidth limiter's parameters are only
>> settable during vif setup time. This patch register a watch on them, and
>> thus makes them runtime changeable.
>>
>> When the watch fires, the timer is reset. The timer's mutex is used for
>> fencing the change.
>>
>
> I think this is a valid idea. Just that this commit message is not
> complete. It doesn't describe everything this patch does.
>
>> Cc: Anthony Liguori <aliguori@...zon.com>
>> Signed-off-by: Imre Palik <imrep@...zon.de>
>> ---
> [...]
>> queue->rx_queue_max = XENVIF_RX_QUEUE_BYTES;
>> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
>> index cab9f52..bcc1880 100644
>> --- a/drivers/net/xen-netback/netback.c
>> +++ b/drivers/net/xen-netback/netback.c
>> @@ -641,7 +641,7 @@ static void tx_add_credit(struct xenvif_queue *queue)
>> queue->remaining_credit = min(max_credit, max_burst);
>> }
>>
>> -static void tx_credit_callback(unsigned long data)
>> +void xenvif_tx_credit_callback(unsigned long data)
>
> Please keep this function static.
The trouble with that, is that now I am initialising credit_timeout.function in
drivers/net/xen-netback/interface.c .
The reason for the change is that mod_timer_pending() hits a BUG() if
the timeout function is not initialised.
>
> And say in the commit message you change tx_credit_callback to a better
> name.
>
>> {
>> struct xenvif_queue *queue = (struct xenvif_queue *)data;
>> tx_add_credit(queue);
>> @@ -1170,7 +1170,7 @@ static bool tx_credit_exceeded(struct xenvif_queue *queue, unsigned size)
>> queue->credit_timeout.data =
>> (unsigned long)queue;
>> queue->credit_timeout.function =
>> - tx_credit_callback;
>> + xenvif_tx_credit_callback;
>> mod_timer(&queue->credit_timeout,
>> next_credit);
> [...]
>> @@ -594,13 +597,9 @@ static void xen_net_read_rate(struct xenbus_device *dev,
>> unsigned long b, u;
>> char *ratestr;
>>
>> - /* Default to unlimited bandwidth. */
>> - *bytes = ~0UL;
>> - *usec = 0;
>> -
>> ratestr = xenbus_read(XBT_NIL, dev->nodename, "rate", NULL);
>> if (IS_ERR(ratestr))
>> - return;
>> + goto reset;
>>
>> s = ratestr;
>> b = simple_strtoul(s, &e, 10);
>> @@ -612,15 +611,21 @@ static void xen_net_read_rate(struct xenbus_device *dev,
>> if ((s == e) || (*e != '\0'))
>> goto fail;
>>
>> + kfree(ratestr);
>> +
>> *bytes = b;
>> *usec = u;
>>
>> - kfree(ratestr);
>> return;
>>
>> - fail:
>> +fail:
>> pr_warn("Failed to parse network rate limit. Traffic unlimited.\n");
>> kfree(ratestr);
>> +
>> +reset:
>> + /* Default to unlimited bandwidth. */
>> + *bytes = ~0UL;
>> + *usec = 0;
>> }
>>
>
> Any reason you modify this function? It is still doing the exact same
> thing, right?
These changes made sense before the channel support, but not anymore.
I will roll them back.
>
>> static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
>> @@ -645,6 +650,59 @@ static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
>> return 0;
>> }
>>
>> +static void xen_net_rate_changed(struct xenbus_watch *watch,
>> + const char **vec, unsigned int len)
>> +{
>> + struct xenvif *vif = container_of(watch, struct xenvif, credit_watch);
>> + struct xenbus_device *dev = xenvif_to_xenbus_device(vif);
>> + unsigned long credit_bytes;
>> + unsigned long credit_usec;
>> + unsigned int queue_index;
>> +
>> + xen_net_read_rate(dev, &credit_bytes, &credit_usec);
>> + for (queue_index = 0; queue_index < vif->num_queues; queue_index++) {
>> + struct xenvif_queue *queue = &vif->queues[queue_index];
>> +
>> + queue->credit_bytes = credit_bytes;
>> + queue->credit_usec = credit_usec;
>> + if (!mod_timer_pending(&queue->credit_timeout, jiffies) &&
>> + queue->remaining_credit > queue->credit_bytes) {
>> + queue->remaining_credit = queue->credit_bytes;
>> + }
>> + }
>> +}
>> +
>> +static int xen_register_watchers(struct xenbus_device *dev, struct xenvif *vif)
>> +{
>> + int err = 0;
>> + char *node;
>> + unsigned maxlen = strlen(dev->nodename) + sizeof("/rate");
>> +
>> + node = kmalloc(maxlen, GFP_KERNEL);
>> + if (!node)
>> + return -ENOMEM;
>> + sprintf(node, "%s/rate", dev->nodename);
>
> Please use snprintf. (Though I can see using sprintf is fine here but I
> want the code to be a bit future proof.)
>
>> + vif->credit_watch.node = node;
>> + vif->credit_watch.callback = xen_net_rate_changed;
>> + err = register_xenbus_watch(&vif->credit_watch);
>> + if (err) {
>> + pr_err("Failed to set watcher %s\n", vif->credit_watch.node);
>> + kfree(node);
>> + vif->credit_watch.node = 0;
>> + vif->credit_watch.callback = 0;
>
> Please use NULL here.
>
> Wei.
>
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