Subject: Re: [Ksummit-2005-discuss] Summary of 2005 Kernel Summit Proposed Topics

From: Matt Mackall <[email-masked]>
Date: Sun, 27 Mar 2005 11:58:46 -0800

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 <[email-masked]> 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.