On Tue, Jun 09, 2015 at 03:04:02PM +0800, Linhaifeng wrote: > > > On 2015/4/24 15:27, Luke Gorrie wrote: > > On 24 April 2015 at 03:01, Linhaifeng <haifeng.lin at 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. >
That's why a correct guest, after detecting an empty used ring, must always re-check used idx at least once after writing avail->flags. By the way, similarly, host side must re-check avail idx after writing used flags. I don't see where snabbswitch does it - is that a bug in snabbswitch? -- MST