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

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Message-ID: <20160509062407.GA2060@nanopsycho.orion>
Date:	Mon, 9 May 2016 08:24:07 +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 10:45:44PM CEST, jiri@...nulli.us wrote:
>Mon, May 02, 2016 at 10:23:27PM CEST, eric.dumazet@...il.com wrote:
>>On Mon, 2016-05-02 at 21:12 +0200, Jiri Pirko wrote:
>>> 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.
>>
>>Interesting.
>>
>>It looks like net/sunrpc/xprtsock.c should set SOCK_FASYNC
>>even if it is not actually using fasync_list
>>
>>Could you try this quick hack to check if this is the right way ?
>
>Yep, works, I do not see the issue with this patch anymore. Thanks.

Eric, any news with this issue?

Thanks.