netdev - Re: [PATCH] tcp: splice as many packets as possible at once

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Date:	Sun, 11 Jan 2009 17:00:37 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Evgeniy Polyakov <zbr@...emap.net>
CC:	Willy Tarreau <w@....eu>, David Miller <davem@...emloft.net>,
	ben@...s.com, jarkao2@...il.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: [PATCH] tcp: splice as many packets as possible at once

Evgeniy Polyakov a écrit :
> On Sun, Jan 11, 2009 at 02:14:57PM +0100, Eric Dumazet (dada1@...mosbay.com) wrote:
>>>> 1) the release_sock/lock_sock done in tcp_splice_read() is not necessary
>>>> to process backlog. Its already done in skb_splice_bits()
>>> Yes, in the tcp_splice_read() they are added to remove a deadlock.
>> Could you elaborate ? A deadlock only if !SPLICE_F_NONBLOCK ?
> 
> Sorry, I meant that we drop lock in skb_splice_bits() to prevent the deadlock,
> and tcp_splice_read() needs it to process the backlog.

While we drop lock in skb_splice_bits() to prevent the deadlock, we
also process backlog at this stage. No need to process backlog
again in the higher level function.

> 
> I think that even with non-blocking splice that release_sock/lock_sock
> is needed, since we are able to do a parallel job: to receive new data
> (scheduled by early release_sock backlog processing) in bh and to
> process already received data via splice codepath.
> Maybe in non-blocking splice mode this is not an issue though, but for
> the blocking mode this allows to grab more skbs at once in skb_splice_bits.

skb_splice_bits() operates on one skb, you lost me :)



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