From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Mackall Subject: Re: [Ksummit-2005-discuss] Summary of 2005 Kernel Summit Proposed Topics Date: Sun, 27 Mar 2005 11:58:46 -0800 Message-ID: <20050327195846.GD15453@waste.org> References: <20050325034341.GV32638@waste.org> <20050327035149.GD4053@g5.random> <20050327054831.GA15453@waste.org> <1111905181.4753.15.camel@mylaptop> <20050326224621.61f6d917.davem@davemloft.net> <1111907130.4753.32.camel@mylaptop> <20050326235712.25f9ca36.davem@davemloft.net> <1111911493.5824.12.camel@mylaptop> <4246FAD5.5080700@cs.wisc.edu> <20050327103115.5c746472.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Mike Christie , open-iscsi@googlegroups.com, andrea@suse.de, James.Bottomley@HansenPartnership.com, ksummit-2005-discuss@thunk.org, netdev@oss.sgi.com To: "David S. Miller" Content-Disposition: inline In-Reply-To: <20050327103115.5c746472.davem@davemloft.net> Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org On Sun, Mar 27, 2005 at 10:31:15AM -0800, David S. Miller wrote: > On Sun, 27 Mar 2005 10:26:29 -0800 > Mike Christie wrote: > > > reliable receive is ciritical for WRITEs. Even if the WRITE is executed > > successfully on the remote device, if we cannot receive the return status > > from the device the operation will fail at the iscsi driver side due to a > > SCSI timeout. > > I keep hearing this word "reliable", it means something very > different for TCP over a transport like IP than it does > for the SCSI layer. This has nothing to do with the specifics of TCP or IP. We are out of memory. To free memory, we must be able to send N packets and receive M acknowledgements. Sending and receiving packets requires allocations - if we cannot allocate, we are permanently wedged. This strongly suggests we need to have private reserves that the network layer knows how to access to fullfill higher level write requests. A closely analogous situation exists with regular SCSI, where the transport is also potentially lossy. (In the iSCSI case, it's somewhat worse: we may need to open a new socket or have one in reserve.) -- Mathematics is the supreme nostalgia of our time.