netdev - Re: [PATCH RFC net-next 2/7] net: add dst_pending

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Date:   Mon, 19 Dec 2016 22:37:50 +0200 (EET)
From:   Julian Anastasov <ja@....bg>
To:     Eric Dumazet <eric.dumazet@...il.com>
cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        YueHaibing <yuehaibing@...wei.com>
Subject: Re: [PATCH RFC net-next 2/7] net: add dst_pending_confirm flag to
 skbuff


	Hello,

On Mon, 19 Dec 2016, Eric Dumazet wrote:

> I am still digesting this awesome patch series ;)

	Thanks. I don't feel quite comfortable with some
of the changes (mostly XFRM, dst_confirm usage in CXGB) and
I hope the discussion can provide adequate solution.

> Not sure why you used an unlikely() here. TCP for example would hit this
> path quite often.

	I was not sure, may be because ACKs can come with lower
rate than the sent packets. Also because non-TCP rarely uses
MSG_CONFIRM. If you still think it is better without unlikely,
I'll remove it.

> So considering sk_dst_pending_confirm might be dirtied quite often,
> 
> I am not sure why you placed it in the cache line that contains
> sk_rx_dst (in 1st patch)

	I saw your recent changes and was worried if the
sk_dst_confirm() calling on RX can cause unwanted dirtying of
additional cache line. My preliminary analyze pointed
sk_omem_alloc as good candidate for moving to next cache
line. I know how critical is to properly place the new flags,
so I really need recommendations about this.

Regards

--
Julian Anastasov <ja@....bg>