From: Eric Dumazet <eric.dumazet@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org, ncardwell@google.com,
therbert@google.com, ycheng@google.com, ak@linux.intel.com
Subject: Re: [PATCH] tcp: avoid wakeups for pure ACK
Date: Wed, 27 Feb 2013 10:17:39 -0800 [thread overview]
Message-ID: <1361989059.11403.50.camel@edumazet-glaptop> (raw)
In-Reply-To: <20130227.130444.2188252064827683663.davem@davemloft.net>
On Wed, 2013-02-27 at 13:04 -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Wed, 27 Feb 2013 09:05:03 -0800
>
> > Processing pure ACK on behalf of the thread blocked in tcp_recvmsg()
> > is a waste of resources, as thread has to immediately sleep again
> > because it got no payload.
>
> More than one thread can be operating on the socket, the other one
> could be waiting for the window to open up in order to do a send. Are
> you absolutely sure that we won't have a problem in that situation?
Yes, more than one thread can be operating, but the prequeue wakeups the
one blocked in tcp_recvmsg() only, because of :
wake_up_interruptible_sync_poll(sk_sleep(sk),
POLLIN | POLLRDNORM | POLLRDBAND);
Then the ACK processing might/should wakeup the other thread blocked in
tcp_sendmsg().
So this patch will also help this (not very usual) situation, as we will
only wakeup the tcp_sendmsg() thread when ACK is processed from softirq
handler, and let the thread blocked in tcp_recvmsg() sleeping.
> In fact I wonder if that does the right thing right now.
Right now it is working, because at least one thread will process the
prequeue at the exit of tcp_recvmsg()
next prev parent reply other threads:[~2013-02-27 18:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-27 17:05 [PATCH] tcp: avoid wakeups for pure ACK Eric Dumazet
2013-02-27 18:04 ` David Miller
2013-02-27 18:17 ` Eric Dumazet [this message]
2013-02-27 21:15 ` David Miller
2013-02-28 20:38 ` David Miller
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