Re: [dpdk-dev] [PATCH] vhost: flush used->idx update before reading avail->flags

[Linhaifeng <haifeng.lin@huawei.com>]

On 2015/4/24 15:27, Luke Gorrie wrote:
> On 24 April 2015 at 03:01, Linhaifeng <haifeng.lin@huawei.com> wrote:
> 
>> If not add memory fence what would happen? Packets loss or interrupt
>> loss?How to test it ?
>>
> 
> You should be able to test it like this:
> 
> 1. Boot two Linux kernel (e.g. 3.13) guests.
> 2. Connect them via vhost switch.
> 3. Run continuous traffic between them (e.g. iperf).
> 
> I would expect that within a reasonable timeframe (< 1 hour) one of the
> guests' network interfaces will hang indefinitely due to a missed interrupt.
> 
> You won't be able to reproduce this using DPDK guests because they are not
> using the same interrupt suppression method.
> 
> This is a serious real-world problem. I wouldn't deploy the vhost
> implementation without this fix.
> 
> Cheers,
> -Luke
> 

I think this patch can't resole this problem. On the other hand we still would miss interrupt.

After add rte_mb() function the we want the case is :
1.write used->idx. ring is full or empty.
2.virtio_net open interrupt.
3.read avail->flags.

but this case(miss interrupt) would happen too:
1.write used->idx. ring is full or empty.
2.read avail->flags.
3.virtio_net open interrupt.