On 2/26/20 1:05 PM, Eli Britstein wrote:
>
> On 2/24/2020 1:06 PM, Ilya Maximets wrote:
>> On 2/23/20 3:32 PM, Eli Britstein wrote:
>>> On 2/21/2020 4:54 PM, Ilya Maximets wrote:
>>>> If the offloading queue is big and filled continuously, offloading
>>>> thread may have no chance to quiesce blocking rcu callbacks and
>>>> other threads waiting for synchronization.
>>>>
>>>> Fix that by entering momentary quiescent state after each operation
>>>> since we're not holding any rcu-protected memory here.
>>>>
>>>> Fixes: 02bb2824e51d ("dpif-netdev: do hw flow offload in a thread")
>>>> Reported-by: Eli Britstein <[email protected]>
>>>> Reported-at:
>>>> https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.openvswitch.org%2Fpipermail%2Fovs-discuss%2F2020-February%2F049768.html&data=02%7C01%7Celibr%40mellanox.com%7C1989a8c52ed74a5b3a6208d7b9199d32%7Ca652971c7d2e4d9ba6a4d149256f461b%7C0%7C0%7C637181391983096010&sdata=eOLfKmc9Xo3APYbOWoajnrvIaUir3A4x4%2BiLc0CbhPI%3D&reserved=0
>>>> Signed-off-by: Ilya Maximets <[email protected]>
>>>> ---
>>>> lib/dpif-netdev.c | 1 +
>>>> 1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
>>>> index d393aab5e..a798db45d 100644
>>>> --- a/lib/dpif-netdev.c
>>>> +++ b/lib/dpif-netdev.c
>>>> @@ -2512,6 +2512,7 @@ dp_netdev_flow_offload_main(void *data OVS_UNUSED)
>>>> VLOG_DBG("%s to %s netdev flow\n",
>>>> ret == 0 ? "succeed" : "failed", op);
>>>> dp_netdev_free_flow_offload(offload);
>>>> + ovsrcu_quiesce();
>>> This seems to solve the issue of responsiveness, but I have encountered a
>>> crash using it, while there is a lot of flow deletions.
>>>
>>> #0 0x0000000001e462dc in get_unaligned_u32 (p=0x7f57f7813500) at
>>> lib/unaligned.h:86
>>> #1 0x0000000001e46388 in hash_bytes (p_=0x7f57f7813500, n=16, basis=0) at
>>> lib/hash.c:38
>>> #2 0x0000000001f7f836 in ufid_to_rte_flow_data_find (ufid=0x7f57f7813500)
>>> at lib/netdev-offload-dpdk.c:134
>>> #3 0x0000000001f88693 in netdev_offload_dpdk_flow_del (netdev=0x42260da0,
>>> ufid=0x7f57f7813500, stats=0x0) at lib/netdev-offload-dpdk.c:3361
>>> #4 0x0000000001e6a00d in netdev_flow_del (netdev=0x42260da0,
>>> ufid=0x7f57f7813500, stats=0x0) at lib/netdev-offload.c:296
>> This might mean 2 things:
>> 1. Incorrect usage of RCU protected data inside netdev-offload-dpdk.
>> 2. We're not allowed to quiesce if we have any item in offloading queue,
>> i.e. bad RCU usage scheme in dpif-netdev.
>>
>> Both cases are bad and I'm not sure if we can easily fix case #2.
>> I'll take a look and try to find a root cause.
>
> It was my bad. Sorry. This is another issue, that exists in my branch only
> (CT offloads), so it's not related. I was able to fix it.
OK. Good to know.
>
> However, I wanted to reproduce with master branch, but then I cannot create a
> lot of flows as I get: "upcall: datapath flow limit reached".
>
> I tried setting large number using "ovs-appctl upcall/set-flow-limit 400000",
> but it didn't help.
Number of flows in dpif-netdev is artificially limited by MAX_FLOWS (65536)
value. There was a recent discussion about this limit and I think we could
just remove it. I have a small patch for this, will send soon.
For now, you can just raise the hardcoded value of MAX_FLOWS in dpif-netdev.c.
>
>>
>>> In other trials, I see the ovs-appctl stuck again, but then I cannot attach
>>> gdb (or use pstack). It hangs. In this scenario, I see this in dmesg:
>>>
>>> [ 404.450694] ovs-vswitchd[8574]: segfault at 7f8bd4e87280 ip
>>> 0000000001e463c3 sp 00007f8cfaf33028 error 4 in ovs-vswitchd[400000+200c000]
>>>
>>> Yanqin Wei <[email protected]> suggested to add ovsrcu_try_quiesce call
>>> (in the same place). It seems more stable (haven't see such crash as
>>> above), but it has the same stuck symptom as above.
>> ovsrcu_try_quiesce() is the same as ovsrcu_quiesce() except that is fails
>> if mutex can not be taken right now. There is no real difference. Your
>> crashes are less frequent just because thread enters quiescent state less
>> frequently.
> If so, I think "ovsrcu_try_quiesce" is more suitable here. Don't you think?
I don't think that taking of one more mutex could make harm in
offloading thread. If we'll want to care about minor sleeping
spikes, we should start from replacing the dp_flow_offload.mutex
and sleeping on the conditional variable.
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