Message-ID: <496A17A5.7010200@cosmosbay.com>
Date: Sun, 11 Jan 2009 17:00:37 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Evgeniy Polyakov <zbr@ioremap.net>
CC: Willy Tarreau <w@1wt.eu>, David Miller <davem@davemloft.net>, ben@zeus.com,
       jarkao2@gmail.com, mingo@elte.hu, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org, jens.axboe@oracle.com
Subject: Re: [PATCH] tcp: splice as many packets as possible at once
References: <20090109185448.GA1999@1wt.eu> <4967B8C5.10803@cosmosbay.com> <20090109212400.GA3727@1wt.eu> <20090109220737.GA4111@1wt.eu> <4967CBB9.1060403@cosmosbay.com> <20090109221744.GA4819@1wt.eu> <20090109224258.GA10257@ioremap.net> <496850D5.8040907@cosmosbay.com> <20090111125759.GB24173@ioremap.net> <4969F0D1.8020504@cosmosbay.com> <20090111133533.GB25337@ioremap.net>
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Evgeniy Polyakov a ?crit :
> On Sun, Jan 11, 2009 at 02:14:57PM +0100, Eric Dumazet (dada1@cosmosbay.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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