[net-next,1/3] hv_netvsc: Use per socket hash when available

From: Haiyang Zhang <haiyangz@microsoft.com>

The per socket hash is set when a socket is connected. Use it, when
available, to save CPU cycles on repeatedly computing hash on the same
connection.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Stephen Hemminger <sthemmin@microsoft.com>
---
 drivers/net/hyperv/netvsc_drv.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

From: Haiyang Zhang <haiyangz@exchange.microsoft.com>
Date: Sat,  8 Apr 2017 17:53:59 -0700

> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index f24c289..0a129cb 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -211,9 +211,14 @@ static u16 netvsc_select_queue(struct net_device *ndev, struct sk_buff *skb,
>  	int q_idx = sk_tx_queue_get(sk);
>  
>  	if (q_idx < 0 || skb->ooo_okay || q_idx >= num_tx_queues) {
> -		u16 hash = __skb_tx_hash(ndev, skb, VRSS_SEND_TAB_SIZE);
> +		u16 hash;
>  		int new_idx;
>  
> +		if (sk)
> +			skb_set_hash_from_sk(skb, sk);
> +
> +		hash = __skb_tx_hash(ndev, skb, VRSS_SEND_TAB_SIZE);

Please do not do this.

TCP performs this operation for you for every pack it emits.

And also every socket family that uses skb_set_owner_w() either
directly or indirectly gets this done as well.

I do not want to see drivers start to get peppered with calls to this
thing.

Explain the case which is missing that matters, and we can address
that instead.

Thanks.

> -----Original Message-----
> From: David Miller [mailto:davem@davemloft.net]
> Sent: Tuesday, April 11, 2017 10:13 PM
> To: Haiyang Zhang <haiyangz@microsoft.com>; Haiyang Zhang
> <haiyangz@microsoft.com>
> Cc: netdev@vger.kernel.org; KY Srinivasan <kys@microsoft.com>;
> olaf@aepfle.de; vkuznets@redhat.com; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH net-next,1/3] hv_netvsc: Use per socket hash when
> available
> 
> From: Haiyang Zhang <haiyangz@exchange.microsoft.com>
> Date: Sat,  8 Apr 2017 17:53:59 -0700
> 
> > diff --git a/drivers/net/hyperv/netvsc_drv.c
> b/drivers/net/hyperv/netvsc_drv.c
> > index f24c289..0a129cb 100644
> > --- a/drivers/net/hyperv/netvsc_drv.c
> > +++ b/drivers/net/hyperv/netvsc_drv.c
> > @@ -211,9 +211,14 @@ static u16 netvsc_select_queue(struct net_device
> *ndev, struct sk_buff *skb,
> >  	int q_idx = sk_tx_queue_get(sk);
> >
> >  	if (q_idx < 0 || skb->ooo_okay || q_idx >= num_tx_queues) {
> > -		u16 hash = __skb_tx_hash(ndev, skb, VRSS_SEND_TAB_SIZE);
> > +		u16 hash;
> >  		int new_idx;
> >
> > +		if (sk)
> > +			skb_set_hash_from_sk(skb, sk);
> > +
> > +		hash = __skb_tx_hash(ndev, skb, VRSS_SEND_TAB_SIZE);
> 
> Please do not do this.
> 
> TCP performs this operation for you for every pack it emits.
> 
> And also every socket family that uses skb_set_owner_w() either
> directly or indirectly gets this done as well.
> 
> I do not want to see drivers start to get peppered with calls to this
> thing.
> 
> Explain the case which is missing that matters, and we can address
> that instead.
> 
> Thanks.

Thanks for pointing this out. I did some tests, the skb->hash is indeed
set to the sk->sk_txhash by upper layer. I will remove this patch, and
re-submit other patches.

Thanks,
- Haiyang