netdev - Re: about latencies

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Message-ID: <alpine.DEB.1.10.0904231803550.28139@qirst.com>
Date:	Thu, 23 Apr 2009 18:06:43 -0400 (EDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	"David S. Miller" <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Michael Chan <mchan@...adcom.com>,
	Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: about latencies

On Fri, 24 Apr 2009, Eric Dumazet wrote:

> sock_wfree()
>   -> sock_def_write_space()
>      -> _read_lock()
>      -> __wake_up_sync_key()
>   and lot of functions calls to wakeup the task, for nothing since it
> will just schedule again. Lot of cache lines dirtied...

Right.

> We could improve this.
>
> 1) dst_release at xmit time, should save a cache line ping-pong on general case
> 2) sock_wfree() in advance, done at transmit time (generally the thread/cpu doing the send)
> 3) changing bnx2_poll_work() to first call bnx2_rx_int(), then bnx2_tx_int() to consume tx.

Good idea that would get rid of the IRQ delay if the process is asking for
data. We'd only be batching if no one is asking for data?

> What do you think ?

Sounds good.
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