netdev - Re: [PATCH] Generalize socket rx gap / receive queue overflow cmsg (v2)

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Date:	Fri, 9 Oct 2009 19:21:40 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, socketcan@...tkopp.net
Subject: Re: [PATCH] Generalize socket rx gap / receive queue overflow cmsg
	(v2)

On Fri, Oct 09, 2009 at 11:31:26PM +0200, Eric Dumazet wrote:
> Neil Horman a écrit :
> 
> >  
> > +extern void __sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk,
> > +	struct sk_buff *skb);
> 
> Surely you meant __sock_recv_drops() ? It only deals with drops.
> 
No, I certainly meant both.  The defintion clearly handles both the timestamp
cmsg and the drops cmsg.  That way we don't need to make two calls in the
receive path for these

> 
> > +	case SO_RXQ_OVFL:
> > +		v.val = sock_flag(sk, SOCK_RXQ_OVFL);
> > +		break;
> > +
> 
> Hmm, I advise to use v.val = !!sock_flag(sk, SOCK_RXQ_OVFL);
> So that application gets 0 or 1, not 0 or some big value.
> Its better because it allows us to change internal SOCK_RXQ_OVFL if necessary in the future.
> 
I don't really see any difference, sock_flag is simply a wrapper around
test_bit.  I can change it if you really need, but it just looks like additional
operations to me

> >  drop_n_acct:
> > -	spin_lock(&sk->sk_receive_queue.lock);
> > -	po->stats.tp_drops++;
> > -	spin_unlock(&sk->sk_receive_queue.lock);
> > +	po->stats.tp_drops = atomic_inc_return(&sk->sk_drops);
> 
> Yes :)
> 
> >  EXPORT_SYMBOL_GPL(__sock_recv_timestamp);
> >  
> > +void __sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk,
> > +	struct sk_buff *skb)
> > +{
> > +	put_cmsg(msg, SOL_SOCKET, SO_RXQ_OVFL, sizeof(__u32), &skb->dropcount);
> > +}
> > +EXPORT_SYMBOL_GPL(__sock_recv_ts_and_drops);
> > +
> 
> Just change the name.
> 
No.  I'm differentiating from sock_recv_timestamp here, as I'm concerned about
the case in which we enqueue to sk_error_queue.  For those cases, in which
recvmsg is called with MSG_ERRQUEUE, I don't think its right to apply a cmsg
based on skb->dropcount, since the frame may have been from a tx path, or may
not have had dropcount set in the first place.  timestamp is still recorded
there, but I don't think we should mark the dropcount.

> And is it really too large to be inlined ?
> 
No, I was just following the style of sock_recv_timestamp.  

> In the contrary, sock_recv_timestamp() is so large that I suspect
> your sock_recv_ts_and_drops should *not* be inlined, and include inlined versions only :
> 
> I suggest something more orthogonal like :
> 
> void inline sock_recv_drops(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
> {
> 	if (sock_flag(sk, SOCK_RXQ_OVFL) && skb && skb->dropcount)
> 		put_cmsg(msg, SOL_SOCKET, SO_RXQ_OVFL,
> 			 sizeof(__u32), &skb->dropcount);
> }
> 
> void sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
> {
> 	sock_recv_timestamp(msg, sk, skb); // inlined
> 	sock_recv_drops(msg, sk, skb); // inlined
> }
> EXPORT_SYMBOL_GPL(sock_recv_ts_and_drops)
Fine.
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