From: David Miller <davem@davemloft.net>
To: steve@digidescorp.com
Cc: netdev@vger.kernel.org, kuznet@ms2.inr.ac.ru, pekkas@netcore.fi,
jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] NET_DMA: free skbs periodically
Date: Thu, 18 Mar 2010 20:36:44 -0700 (PDT) [thread overview]
Message-ID: <20100318.203644.102533317.davem@davemloft.net> (raw)
In-Reply-To: <1268752964-4397-1-git-send-email-steve@digidescorp.com>
From: "Steven J. Magnani" <steve@digidescorp.com>
Date: Tue, 16 Mar 2010 10:22:44 -0500
> Under NET_DMA, data transfer can grind to a halt when userland issues a
> large read on a socket with a high RCVLOWAT (i.e., 512 KB for both).
> This appears to be because the NET_DMA design queues up lots of memcpy
> operations, but doesn't issue or wait for them (and thus free the
> associated skbs) until it is time for tcp_recvmesg() to return.
> The socket hangs when its TCP window goes to zero before enough data is
> available to satisfy the read.
>
> Periodically issue asynchronous memcpy operations, and free skbs for ones
> that have completed, to prevent sockets from going into zero-window mode.
>
> Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Can one of the NET DMA folks review this.
It's a pretty fundamental problem with how this stuff works
it seems.
next prev parent reply other threads:[~2010-03-19 3:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-16 15:22 [PATCH] NET_DMA: free skbs periodically Steven J. Magnani
2010-03-19 3:36 ` David Miller [this message]
2010-03-20 21:29 ` David Miller
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