[PATCH] vhost: use try_lock in rte_vhost_vring_call

[Maxime Coquelin]

On 9/20/22 04:53, Xia, Chenbo wrote:
>> -----Original Message-----
>> From: Liu, Changpeng <changpeng.liu at intel.com>
>> Sent: Tuesday, September 20, 2022 10:34 AM
>> To: Xia, Chenbo <chenbo.xia at intel.com>; dev at dpdk.org
>> Cc: Maxime Coquelin <maxime.coquelin at redhat.com>
>> Subject: RE: [PATCH] vhost: use try_lock in rte_vhost_vring_call
>>
>> Hi Bo,
>>
>>> -----Original Message-----
>>> From: Xia, Chenbo <chenbo.xia at intel.com>
>>> Sent: Tuesday, September 20, 2022 10:25 AM
>>> To: Liu, Changpeng <changpeng.liu at intel.com>; dev at dpdk.org
>>> Cc: Maxime Coquelin <maxime.coquelin at redhat.com>
>>> Subject: RE: [PATCH] vhost: use try_lock in rte_vhost_vring_call
>>>
>>> Hi Changpeng,
>>>
>>>> -----Original Message-----
>>>> From: Liu, Changpeng <changpeng.liu at intel.com>
>>>> Sent: Tuesday, September 6, 2022 10:22 AM
>>>> To: dev at dpdk.org
>>>> Cc: Liu, Changpeng <changpeng.liu at intel.com>; Maxime Coquelin
>>>> <maxime.coquelin at redhat.com>; Xia, Chenbo <chenbo.xia at intel.com>
>>>> Subject: [PATCH] vhost: use try_lock in rte_vhost_vring_call
>>>>
>>>> Note that this function is in data path, so the thread context
>>>> may not same as socket messages processing context, by using
>>>> try_lock here, users can have another try in case of VQ's access
>>>> lock is held by `vhost-events` thread.
>>>
>>> Better to describe the issue this patch wants to fix and how does
>>> it fix.
>>>
>>> I remember it's a bz issue, do you want to backport? And it has
>>> some bz ID, we need to add it in commit message.
>> Actually it's my intention not to add bz ID, as I think for this bz ID,
>> It's better not to lock all VQ's access lock for KICK/CALLFD messages,
> 
> Do you plan to add this change? I think that may be an improvement to current
> locking implementation.
> 
> Maxime, what do you think of this idea about only locking specific queue when
> handling vring related message (not global config like mem table)?

I think this is not a good idea.
For example SET_VRING_KICK can currently call
translate_ring_addresses(), which itself can call numa_realloc().

numa_realloc() may reallocate the dev, so you don't want it to be used
by other queues while it happens.

>> What do you think? If this is identified as a fix, I can backport it to
>> 22.05.
> 
> You can decide, if this is planned to be the fix, just backport. I am just
> thinking if this is not the fix for the bz, do we still need this?
> 
> Thanks,
> Chenbo
> 
>>>
>>>>
>>>> Signed-off-by: Changpeng Liu <changpeng.liu at intel.com>
>>>> ---
>>>>   lib/vhost/vhost.c | 6 +++++-
>>>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
>>>> index 60cb05a0ff..072d2acb7b 100644
>>>> --- a/lib/vhost/vhost.c
>>>> +++ b/lib/vhost/vhost.c
>>>> @@ -1329,7 +1329,11 @@ rte_vhost_vring_call(int vid, uint16_t
>> vring_idx)
>>>>   	if (!vq)
>>>>   		return -1;
>>>>
>>>> -	rte_spinlock_lock(&vq->access_lock);
>>>> +	if (!rte_spinlock_trylock(&vq->access_lock)) {
>>>> +		VHOST_LOG_CONFIG(dev->ifname, DEBUG,
>>>
>>> Should use VHOST_LOG_DATA
>> OK.
>>>
>>> Thanks,
>>> Chenbo
>>>
>>>> +			"failed to kick guest, virtqueue busy.\n");
>>>> +		return -1;
>>>> +	}
>>>>
>>>>   	if (vq_is_packed(dev))
>>>>   		vhost_vring_call_packed(dev, vq);
>>>> --
>>>> 2.21.3
>