From mboxrd@z Thu Jan 1 00:00:00 1970 In-Reply-To: <000f01c48a95$e18e5c20$0301a8c0@chuck2> References: <000f01c48a95$e18e5c20$0301a8c0@chuck2> Mime-Version: 1.0 (Apple Message framework v619) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: Cc: "Embedded Linux PPC list" , "Robert P. J. Day" From: Dan Malek Subject: Re: value of XIP? and whether it works with 2.6 kernel? Date: Wed, 25 Aug 2004 11:32:37 -0400 To: "Mark Chambers" Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: On Aug 25, 2004, at 7:22 AM, Mark Chambers wrote: > The main value, I believe, is as part of a rapid boot setup - you can > avoid the decompress and copy phase. The XIP has little effect on this. Wolfgang hit the important points. I originally did XIP on the 8xx many years ago for an embedded appliance that was DRAM challenged. It saved a little memory, but along with it came the pinned TLB which helped a little with performance. The kernel code was tightly integrated with the initialization code. This is where the start up time was reduced. The initialization code was minimal, and it also immediately put up some graphics on the screen which made the user aware the appliance was "doing something." After minimal part set up, the kernel then started running was modified to continue the screen update as it booted. In the end, it really didn't boot much faster, but at least the activity on the screen was psychologically useful :-) The three big things that slow down the boot process are serial console output (which can be many seconds), timeouts in the boot code waiting for user input, and diagnostic tests (testing memory, checksum of images in flash, etc.) With the large amount of memory in all systems these days, XIP does nothing to help that. The XIP on its own doesn't do anything to speed up the operation of the system. In the whole of a system design XIP can be a useful tool, but just enabling the option without any larger problem to solve is just entertaining, not very useful :-) Thanks. -- Dan ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/