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Message-ID: <496A17A5.7010200@cosmosbay.com>
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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