netdev - Re: [PATCH net-next 1/2] net: SOCKWQ_ASYNC

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Date:	Mon, 2 May 2016 21:12:29 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	"David S . Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, eladr@...lanox.com,
	idosch@...lanox.com
Subject: Re: [PATCH net-next 1/2] net: SOCKWQ_ASYNC_NOSPACE optimizations

Mon, May 02, 2016 at 06:22:18PM CEST, eric.dumazet@...il.com wrote:
>On Mon, 2016-05-02 at 18:16 +0200, Jiri Pirko wrote:
>> Mon, Apr 25, 2016 at 07:39:32PM CEST, edumazet@...gle.com wrote:
>> >SOCKWQ_ASYNC_NOSPACE is tested in sock_wake_async()
>> >so that a SIGIO signal is sent when needed.
>> >
>> >tcp_sendmsg() clears the bit.
>> >tcp_poll() sets the bit when stream is not writeable.
>> >
>> >We can avoid two atomic operations by first checking if socket
>> >is actually interested in the FASYNC business (most sockets in
>> >real applications do not use AIO, but select()/poll()/epoll())
>> >
>> >This also removes one cache line miss to access sk->sk_wq->flags
>> >in tcp_sendmsg()
>> >
>> >Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>> 
>> I just bisected down to this. This is causing a regression for me when
>> my nfs mount becomes stuck. I can easily reproduce this if you need to
>> test the fix.
>
>What do you mean by 'when nfs mount becomes stuck' ?
>
>Is this patch making nfs not functional , or does it make recovery from
>some nfs error bad ?

I can mount nfs on the host. But when I do something (compile a kernel
module in my case), it gets stuck. Then I cannot even ssh to the machine.
No messages in dmesg. I didn't debug it any further. I just bisected and
verified that this patch caused this behaviour.