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

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Message-ID: <66438fad-d697-4b34-89de-528bd5e081b5@daynix.com>
Date: Fri, 27 Sep 2024 11:22:59 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Simon Horman <horms@...nel.org>
Cc: Jonathan Corbet <corbet@....net>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Jason Wang <jasowang@...hat.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, kvm@...r.kernel.org,
 virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org,
 Yuri Benditovich <yuri.benditovich@...nix.com>,
 Andrew Melnychenko <andrew@...nix.com>,
 Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com
Subject: Re: [PATCH RFC v4 7/9] tun: Introduce virtio-net RSS

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@...nix.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