Re: [dpdk-dev] [PATCH v2 0/4] vhost: add missing barriers, move prefetching

[Ilya Maximets <i.maximets@samsung.com>]

On 19.12.2018 18:50, Michael S. Tsirkin wrote:
> On Wed, Dec 19, 2018 at 09:21:09AM +0100, Maxime Coquelin wrote:
>> This series adds missing read barriers after reading avail index
>> for split ring and desc flags for packed ring.
>>
>> Also, it turns out that some descriptors prefetching are either
>> badly placed, or useless, last part of the series fixes that.
>>
>> With the series applied, I get between 0 and 4% gain depending
>> on the benchmark (testpmd txonly/rxonly/io).
>>
>> Thanks to Jason for reporting the missing read barriers.
> 
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> 
> But I wonder what effect this has on ARM where RMB isn't a NOP.
> Ilya do you happen to have any data?

Hi.
My rough testing shows no significant performance difference on ARMv8.

> 
>> Changes since v1:
>> =================
>> - Drop volatile removal patch (Ilya)
>> - Improve commit messages for RMB patches (Ilya)
>>
>> Maxime Coquelin (4):
>>   vhost: enforce avail index and desc read ordering
>>   vhost: enforce desc flags and content read ordering
>>   vhost: prefetch descriptor after the read barrier
>>   vhost: remove useless prefetch for packed ring descriptor
>>
>>  lib/librte_vhost/virtio_net.c | 27 ++++++++++++++++++++++-----
>>  1 file changed, 22 insertions(+), 5 deletions(-)
>>
>> -- 
>> 2.17.2
> 
>