From: Eric Dumazet <dada1@cosmosbay•com>
To: David Miller <davem@davemloft•net>
Cc: kchang@athenacr•com, netdev@vger•kernel.org,
cl@linux-foundation•org, bmb@athenacr•com
Subject: Re: Multicast packet loss
Date: Fri, 13 Mar 2009 23:30:31 +0100 [thread overview]
Message-ID: <49BADE87.40407@cosmosbay.com> (raw)
In-Reply-To: <20090313.145152.121603300.davem@davemloft.net>
David Miller a écrit :
> From: Eric Dumazet <dada1@cosmosbay•com>
> Date: Mon, 09 Mar 2009 07:36:57 +0100
>
>> I chose cmpxchg() because I needed some form of exclusion here.
>> I first added a spinlock inside "struct softirq_del" then I realize
>> I could use cmpxchg() instead and keep the structure small. As the
>> synchronization is only needed at queueing time, we could pass
>> the address of a spinlock XXX to sofirq_del() call.
>
> I don't understand why you need the mutual exclusion in the
> first place. The function pointer always has the same value.
> And this locking isn't protecting the list insertion either,
> as that isn't even necessary.
>
> It just looks like plain overhead to me.
I was lazy to check all callers (all protocols) had a lock on sock,
and prefered safety.
I was fooled by the read_lock(), and though several cpus could call
this function in //
>
>> Also, when an event was queued for later invocation, I also needed to keep
>> a reference on "struct socket" to make sure it doesnt disappear before
>> the invocation. Not all sockets are RCU guarded (we added RCU only for
>> some protocols (TCP, UDP ...). So I found keeping a read_lock
>> on callback was the easyest thing to do. I now realize we might
>> overflow preempt_count, so special care is needed.
>
> You're using this in UDP so... make the rule that you can't use
> this with a non-RCU-quiescent protocol.
UDP/TCP only ? I though many other protocols (not all using RCU) were
using sock_def_readable() too...
next prev parent reply other threads:[~2009-03-13 22:31 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-30 17:49 Multicast packet loss Kenny Chang
2009-01-30 19:04 ` Eric Dumazet
2009-01-30 19:17 ` Denys Fedoryschenko
2009-01-30 20:03 ` Neil Horman
2009-01-30 22:29 ` Kenny Chang
2009-01-30 22:41 ` Eric Dumazet
2009-01-31 16:03 ` Neil Horman
2009-02-02 16:13 ` Kenny Chang
2009-02-02 16:48 ` Kenny Chang
2009-02-03 11:55 ` Neil Horman
2009-02-03 15:20 ` Kenny Chang
2009-02-04 1:15 ` Neil Horman
2009-02-04 16:07 ` Kenny Chang
2009-02-04 16:46 ` Wesley Chow
2009-02-04 18:11 ` Eric Dumazet
2009-02-05 13:33 ` Neil Horman
2009-02-05 13:46 ` Wesley Chow
2009-02-05 13:29 ` Neil Horman
2009-02-01 12:40 ` Eric Dumazet
2009-02-02 13:45 ` Neil Horman
2009-02-02 16:57 ` Eric Dumazet
2009-02-02 18:22 ` Neil Horman
2009-02-02 19:51 ` Wes Chow
2009-02-02 20:29 ` Eric Dumazet
2009-02-02 21:09 ` Wes Chow
2009-02-02 21:31 ` Eric Dumazet
2009-02-03 17:34 ` Kenny Chang
2009-02-04 1:21 ` Neil Horman
2009-02-26 17:15 ` Kenny Chang
2009-02-28 8:51 ` Eric Dumazet
2009-03-01 17:03 ` Eric Dumazet
2009-03-04 8:16 ` David Miller
2009-03-04 8:36 ` Eric Dumazet
2009-03-07 7:46 ` Eric Dumazet
2009-03-08 16:46 ` Eric Dumazet
2009-03-09 2:49 ` David Miller
2009-03-09 6:36 ` Eric Dumazet
2009-03-13 21:51 ` David Miller
2009-03-13 22:30 ` Eric Dumazet [this message]
2009-03-13 22:38 ` David Miller
2009-03-13 22:45 ` Eric Dumazet
2009-03-14 9:03 ` [PATCH] net: reorder fields of struct socket Eric Dumazet
2009-03-16 2:59 ` David Miller
2009-03-16 22:22 ` Multicast packet loss Eric Dumazet
2009-03-17 10:11 ` Peter Zijlstra
2009-03-17 11:08 ` Eric Dumazet
2009-03-17 11:57 ` Peter Zijlstra
2009-03-17 15:00 ` Brian Bloniarz
2009-03-17 15:16 ` Eric Dumazet
2009-03-17 19:39 ` David Stevens
2009-03-17 21:19 ` Eric Dumazet
2009-04-03 19:28 ` Brian Bloniarz
2009-04-05 13:49 ` Eric Dumazet
2009-04-06 21:53 ` Brian Bloniarz
2009-04-06 22:12 ` Brian Bloniarz
2009-04-07 20:08 ` Brian Bloniarz
2009-04-08 8:12 ` Eric Dumazet
2009-03-09 22:56 ` Brian Bloniarz
2009-03-10 5:28 ` Eric Dumazet
2009-03-10 23:22 ` Brian Bloniarz
2009-03-11 3:00 ` Eric Dumazet
2009-03-12 15:47 ` Brian Bloniarz
2009-03-12 16:34 ` Eric Dumazet
2009-02-27 18:40 ` Christoph Lameter
2009-02-27 18:56 ` Eric Dumazet
2009-02-27 19:45 ` Christoph Lameter
2009-02-27 20:12 ` Eric Dumazet
2009-02-27 21:36 ` Eric Dumazet
2009-02-02 13:53 ` Eric Dumazet
-- strict thread matches above, loose matches on Subject: below --
2009-04-05 14:42 bmb
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