Re: [PATCH RFC v4 7/9] tun: Introduce virtio-net RSS

Akihiko Odaki
2024-09-27T02:23:04Z

On 2024/09/24 22:05, Simon Horman wrote:
> On Tue, Sep 24, 2024 at 11:01:12AM +0200, Akihiko Odaki wrote:
>> RSS is a receive steering algorithm that can be negotiated to use with
>> virtio_net. Conventionally the hash calculation was done by the VMM.
>> However, computing the hash after the queue was chosen defeats the
>> purpose of RSS.
>>
>> Another approach is to use eBPF steering program. This approach has
>> another downside: it cannot report the calculated hash due to the
>> restrictive nature of eBPF steering program.
>>
>> Introduce the code to perform RSS to the kernel in order to overcome
>> thse challenges. An alternative solution is to extend the eBPF steering
>> program so that it will be able to report to the userspace, but I didn't
>> opt for it because extending the current mechanism of eBPF steering
>> program as is because it relies on legacy context rewriting, and
>> introducing kfunc-based eBPF will result in non-UAPI dependency while
>> the other relevant virtualization APIs such as KVM and vhost_net are
>> UAPIs.
>>
>> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>
> ...
>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>
> ...
>
>> @@ -333,8 +336,10 @@ static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp)
>> return -EFAULT;
>>
>> if (be) {
>> + struct tun_vnet_hash_container *vnet_hash = rtnl_dereference(tun->vnet_hash);
>> +
>> if (!(tun->flags & TUN_VNET_LE) &&
>> - (tun->vnet_hash.flags & TUN_VNET_HASH_REPORT))
>> + vnet_hash && (vnet_hash->flags & TUN_VNET_HASH_REPORT))
>
> Hi Odaki-san,
>
> I am wondering if the above should this be vnet_hash->common.flags?
> I am seeing this:
>
> ../drivers/net/tun.c:342:44: error: ‘struct tun_vnet_hash_container’ has no member named ‘flags’
> 342 | vnet_hash && (vnet_hash->flags & TUN_VNET_HASH_REPORT))
>
> ...

You are right. I couldn't notice this error because I was testing
without CONFIG_TUN_VNET_CROSS_LE; I'll test with the configuration and
submit a new version with fix.

Regards,
Akihiko Odaki