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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] xennet: skb rides the rocket: 20 slots
Tuesday, January 8, 2013, 3:12:33 AM, you wrote:
> On 2013-1-7 18:55, Ian Campbell wrote:
>> On Fri, 2013-01-04 at 16:28 +0000, Sander Eikelenboom wrote:
>>> Hi Ian,
>> I'm not actually the netfront maintainer. Adding Konrad. Annie too since
>> IIRC she was at one point looking at various buffer coalescing schemes.
>>
>>> Today i fired up an old VM with a bittorrent client, trying to
>>> download some torrents.
>> How old? Which kernel?
>>
>>> I seem to be hitting the unlikely case of "xennet: skb rides the
>>> rocket: xx slots" and this results in some dropped packets in domU, I
>>> don't see any warnings in dom0.
> If debug is enabled, following netback code should print out messages in
> netbk_count_requests.
> if (unlikely(frags >= MAX_SKB_FRAGS)) {
> netdev_dbg(vif->dev, "Too many frags\n");
> return -frags;
> }
I have added some rate limited warns in this function. However none seems to be
triggered while the pv-guest reports the "skb rides the rocket" ..
diff --git a/drivers/net/xen-netback/netback.c
b/drivers/net/xen-netback/netback.c
index f2d6b78..2f02da9 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -902,11 +902,13 @@ static int netbk_count_requests(struct xenvif *vif,
do {
if (frags >= work_to_do) {
netdev_dbg(vif->dev, "Need more frags\n");
+ net_warn_ratelimited("%s: Need more frags:%d,
work_to_do:%d \n",vif->dev->name, frags, work_to_do);
return -frags;
}
if (unlikely(frags >= MAX_SKB_FRAGS)) {
netdev_dbg(vif->dev, "Too many frags\n");
+ net_warn_ratelimited("%s: Too many frags:%d,
MAX_SKB_FRAGS:%d \n",vif->dev->name, frags, MAX_SKB_FRAGS);
return -frags;
}
@@ -914,6 +916,7 @@ static int netbk_count_requests(struct xenvif *vif,
sizeof(*txp));
if (txp->size > first->size) {
netdev_dbg(vif->dev, "Frags galore\n");
+ net_warn_ratelimited("%s: Frags galore:%d,
txp->size:%d first->size:%d\n",vif->dev->name, frags, txp->size , first->size);
return -frags;
}
@@ -923,6 +926,7 @@ static int netbk_count_requests(struct xenvif *vif,
if (unlikely((txp->offset + txp->size) > PAGE_SIZE)) {
netdev_dbg(vif->dev, "txp->offset: %x, size: %u\n",
txp->offset, txp->size);
+ net_warn_ratelimited("%s: Hmm:%d, (txp->offset +
txp->size):%d PAGE_SIZE:%d\n",vif->dev->name, frags, (txp->offset +
txp->size) ,PAGE_SIZE);
return -frags;
}
} while ((txp++)->flags & XEN_NETTXF_more_data);
>>>
>>> I have added some extra info, but i don't have enough knowledge if
>>> this could/should be prevented from happening ?
>> MAX_SKB_FRAGS has never, AFAIK, been as big as 19 or 20 so I'm not sure
>> this can have ever worked.
>>
>> These SKBs seem to be pretty big (not quite 64KB), seemingly most of the
>> data is contained in a smallish number of frags, which suggests compound
>> pages and therefore a reasonably modern kernel?
>>
>> This probably relates somewhat to the issues described in the
>> "netchannel vs MAX_SKB_FRAGS" thread last year, or at least the solution
>> to that would necessarily involve fixing this issue.
> If netback complains about "Too many frags", then it should be
> MAX_SKB_FRAGS limitation in netback results in dropping packets in
> netfront. It is possible that other netfronts(windows?) also hit this.
> Thanks
> Annie
>>
>> In the meantime you could try disabling sg and/or various offloads for
>> that domain's vif.
>>
>>> [16798.629141] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4
>>> page_size:4096 prot:0800
>>> [16800.575182] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:2154 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4
>>> page_size:4096 prot:0800
>>> [16801.589166] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:19 offset:2154 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:5
>>> page_size:4096 prot:0800
>>> [16803.279039] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:3
>>> page_size:4096 prot:0800
>>> [16809.973268] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:2154 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4
>>> page_size:4096 prot:0800
>>> [16811.420048] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:2154 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:6
>>> page_size:4096 prot:0800
>>> [16814.872686] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:5
>>> page_size:4096 prot:0800
>>> [16815.359099] xennet: skb rides the rocket: 21 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:20 offset:2154 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:5
>>> page_size:4096 prot:0800
>>> [16825.851906] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:19 offset:106 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4
>>> page_size:4096 prot:0800
>>> [16828.295083] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:2154 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:5
>>> page_size:4096 prot:0800
>>> [16837.386684] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4
>>> page_size:4096 prot:0800
>>> [16838.609683] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:19 offset:106 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4
>>> page_size:4096 prot:0800
>>> [16841.783729] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:6
>>> page_size:4096 prot:0800
>>> [16843.841678] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:19 offset:2154 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4
>>> page_size:4096 prot:0800
>>> [16849.847614] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:18 offset:3690 skb_headlen:54
>>> skb->len:64294, skb->data_len:64240 skb->truesize:65008 nr_frags:4
>>> page_size:4096 prot:0800
>>> [16853.787128] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17
>>> div_roundup:1 xennet_count_skb_frag_slots:19 offset:2154 skb_headlen:1622
>>> skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4
>>> page_size:4096 prot:0800
>>>
>>> # ifconfig
>>> eth0 Link encap:Ethernet HWaddr 00:16:3e:c4:20:46
>>> inet addr:192.168.1.12 Bcast:192.168.1.255 Mask:255.255.255.0
>>> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
>>> RX packets:9090214 errors:0 dropped:0 overruns:0 frame:0
>>> TX packets:5902090 errors:0 dropped:304 overruns:0 carrier:0
>>> collisions:0 txqueuelen:1000
>>> RX bytes:19757934770 (18.4 GiB) TX bytes:16855238200 (15.6 GiB)
>>> Interrupt:25
>>>
>>>
>>>
>>>
>>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
>>> index c26e28b..50ac403 100644
>>> --- a/drivers/net/xen-netfront.c
>>> +++ b/drivers/net/xen-netfront.c
>>> @@ -552,7 +552,11 @@ static int xennet_start_xmit(struct sk_buff *skb,
>>> struct net_device *dev)
>>> xennet_count_skb_frag_slots(skb);
>>> if (unlikely(slots> MAX_SKB_FRAGS + 1)) {
>>> net_alert_ratelimited(
>>> - "xennet: skb rides the rocket: %d slots\n", slots);
>>> + "xennet: skb rides the rocket: %d slots
>>> MAX_SKB_FRAGS: %d div_roundup:%d xennet_count_skb_frag_slots:%d offset:%d
>>> skb_headlen:%d skb->len:%d, skb->data_len:%d skb->truesize:%d nr_frags:%d
>>> page_size:%d prot:%04x \n
>>> + slots, MAX_SKB_FRAGS,DIV_ROUND_UP(offset +
>>> len, PAGE_SIZE),
>>> + xennet_count_skb_frag_slots(skb), offset,
>>> len, skb->len,
>>> + skb->data_len, skb->truesize,
>>> skb_shinfo(skb)->nr_frags,
>>> + PAGE_SIZE, ntohs(skb->protocol));
>>> goto drop;
>>> }
>>>
>>
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