From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David S. Miller" Subject: Re: slow tcp acks on loopback device Date: Fri, 22 Jul 2005 13:08:16 -0700 (PDT) Message-ID: <20050722.130816.91445335.davem@davemloft.net> References: <1122062219.29258.12.camel@stevef95.austin.ibm.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, samba-technical@lists.samba.org, linux-kernel@vger.kernel.org Return-path: To: smfltc@us.ibm.com In-Reply-To: <1122062219.29258.12.camel@stevef95.austin.ibm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: samba-technical-bounces+gnsi-samba-technical=m.gmane.org@lists.samba.org Errors-To: samba-technical-bounces+gnsi-samba-technical=m.gmane.org@lists.samba.org List-Id: netdev.vger.kernel.org From: Steve French Date: 22 Jul 2005 14:56:59 -0500 > Noticing that the loopback device (at least on RHEL4) has an unfortunate > mtu size 16384 (which is about 50 bytes too small for SMB read > responses), I did try increasing the MTU slightly. Changing that to > 18000 did avoid the fragmentation and the 40ms delay - but what puzzled > me was why setting TCP_NODELAY after the socket was created did not > eliminate the delay on the ack and if there is a way to avoid the huge > tcp ack delay by either doing something else to force client acking > immediately or to do something on the client side of the stack to get > the server to send the whole 16K+ frame - it looks like the tcp windows > is 32K if the value in the tcp acks in the network trace is to be > trusted. TCP_NODELAY does not control ACK generation, instead it modifies the Nagle algorithm behavior when sending data packets. Please take networking discussions to netdev@vger.kernel.org which is where the networking developers are.