> On May 30, 2023, at 11:35 PM, Jason Wang <jasow...@redhat.com> wrote:
>
> On Wed, May 31, 2023 at 11:32 AM Jason Wang <jasow...@redhat.com> wrote:
>>
>> On Wed, May 31, 2023 at 11:17 AM Jon Kohler <j...@nutanix.com> wrote:
>>>
>>> If kernel supports IFF_NAPI, lets use it, which is especially useful
>>> on kernels containing fb3f903769e8 ("tun: support NAPI for packets
>>> received from batched XDP buffs"), as IFF_NAPI allows the
>>> vhost_tx_batch path to use NAPI on XDP buffs.
>>>
>>> Benchmark w/ iperf -c (remote srv) -P (thread count) -l (stream size)
>>> from a guest running kernel 5.10.105 to remote bare metal running
>>> patched code on kernel 5.10.139. Guests were configured 1x virtio-net
>>> device with 4x queues, resulting in 4x vhost-worker threads. Hosts are
>>> identical with Intel ICX 4314 @ 2.4 GHz with Mellanox CX5 25GbE NIC ->
>>> Arista 25GbE switch. vhost-worker threads largely maxed out on CPU on
>>> "Before" and around ~50-60% utilization "After".
>>>
>>> Single Stream: iperf -P 1
>>> iperf -l size | Before | After | Increase
>>> 64B | 593 Mbits/sec | 712 Mbits/sec | ~20%
>>> 128B | 1.00 Gbits/sec | 1.18 Gbits/sec | ~18%
>>> 4KB | 17.6 Gbits/sec | 22.7 Gbits/sec | ~29%
>>>
>>> Multiple Stream: iperf -P 12
>>> iperf -l size | Before | After | Increase
>>> 64B | 6.35 Gbits/sec | 7.78 Gbits/sec | ~23%
>>> 128B | 10.8 Gbits/sec | 14.2 Gbits/sec | ~31%
>>> 4KB | 23.6 Gbits/sec | 23.6 Gbits/sec | (line speed)
>>>
>>> Signed-off-by: Jon Kohler <j...@nutanix.com>
>>
>> Great, but I would suggest having an option.
>>
>> So we can:
>>
>> 1) ease the debug and compare
>> 2) enable this by default only for 8.1, disable it for pre 8.1
Fair enough, one favor to ask though -
Would you be able to point me to an existing option like what you’re
proposing so I could make sure I’m on the same page?
>
> More thought, if the performance boost only after fb3f903769e8, we
> probably need to disable it by default and let the mgmt layer to
> enable it.
>
I focused my testing with that commit, but I could take it out and
we still should get benefit. Would you like me to profile that to validate?
Asking as NAPI support in tun.c has been there for a while, guessing
at first glance that there would be non-zero gains, with little downsides.
Looking at git blame, seems about ~5-6 years of support.
Also for posterity, that commit has been in since 5.18, so a little over 1 year.
> Thanks
>
>>
>> Thanks
>>
>> Thanks
>>
>>> ---
>>> net/tap-linux.c | 4 ++++
>>> net/tap-linux.h | 1 +
>>> 2 files changed, 5 insertions(+)
>>>
>>> diff --git a/net/tap-linux.c b/net/tap-linux.c
>>> index f54f308d359..fd94df166e0 100644
>>> --- a/net/tap-linux.c
>>> +++ b/net/tap-linux.c
>>> @@ -62,6 +62,10 @@ int tap_open(char *ifname, int ifname_size, int
>>> *vnet_hdr,
>>> ifr.ifr_flags |= IFF_ONE_QUEUE;
>>> }
>>>
>>> + if (features & IFF_NAPI) {
>>> + ifr.ifr_flags |= IFF_NAPI;
>>> + }
>>> +
>>> if (*vnet_hdr) {
>>> if (features & IFF_VNET_HDR) {
>>> *vnet_hdr = 1;
>>> diff --git a/net/tap-linux.h b/net/tap-linux.h
>>> index bbbb62c2a75..f4d8e55270b 100644
>>> --- a/net/tap-linux.h
>>> +++ b/net/tap-linux.h
>>> @@ -37,6 +37,7 @@
>>>
>>> /* TUNSETIFF ifr flags */
>>> #define IFF_TAP 0x0002
>>> +#define IFF_NAPI 0x0010
>>> #define IFF_NO_PI 0x1000
>>> #define IFF_ONE_QUEUE 0x2000
>>> #define IFF_VNET_HDR 0x4000
>>> --
>>> 2.30.1 (Apple Git-130)
