My experiences with Qemu - Part II

So I've managed to get this far with Qemu:

(qemu) Uncompressing Linux......................................................... done, booting the kernel.
Linux version 2.6.20.6 (cfriedt@sith) (gcc version 3.4.4) #35 Thu May 31 21:57:50 CEST 2007
CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00003137
Machine: ARM-Versatile PB
Memory policy: ECC disabled, Data cache writeback
CPU0: D VIVT write-through cache
CPU0: I cache: 4096 bytes, associativity 4, 32 byte lines, 32 sets
CPU0: D cache: 65536 bytes, associativity 4, 32 byte lines, 512 sets
Built 1 zonelists. Total pages: 65024
Kernel command line: root=/dev/nfs nfsroot=192.168.7.1:/usr/gentoo_root,uid=0,gid=0,rsize=32768,wsize=32768,timeo=14,nfsvers=3,rw rw ip=192.168.7.2:192.168.7.1:192.168.7.1:255.255.255.0:qemu console=ttyAMA0,115200
PID hash table entries: 1024 (order: 10, 4096 bytes)
Console: colour dummy device 80x30
Dentry cache hash table entries: 32768 (order: 5, 131072 bytes)
Inode-cache hash table entries: 16384 (order: 4, 65536 bytes)
Memory: 256MB = 256MB total
Memory: 258048KB available (1516K code, 174K data, 100K init)
Mount-cache hash table entries: 512
CPU: Testing write buffer coherency: ok
NET: Registered protocol family 16
PCI core found (slot 11)
PCI: bus0: Fast back to back transfers disabled
PCI map irq: slot 0, pin 1, devslot 12, irq: 27
NET: Registered protocol family 2
IP route cache hash table entries: 2048 (order: 1, 8192 bytes)
TCP established hash table entries: 8192 (order: 3, 32768 bytes)
TCP bind hash table entries: 4096 (order: 2, 16384 bytes)
TCP: Hash tables configured (established 8192 bind 4096)
TCP reno registered
NetWinder Floating Point Emulator V0.97 (double precision)
CLCD: unknown LCD panel ID 0x00001000, using VGA
CLCD: Versatile hardware, VGA display
Clock CLCDCLK: setting VCO reg params: S=1 R=99 V=98
Console: switching to colour frame buffer device 80x30
Serial: AMBA PL011 UART driver
dev:f1: ttyAMA0 at MMIO 0x101f1000 (irq = 12) is a AMBA/PL011
dev:f2: ttyAMA1 at MMIO 0x101f2000 (irq = 13) is a AMBA/PL011
dev:f3: ttyAMA2 at MMIO 0x101f3000 (irq = 14) is a AMBA/PL011
fpga:09: ttyAMA3 at MMIO 0x10009000 (irq = 38) is a AMBA/PL011
tun: Universal TUN/TAP device driver, 1.6
tun: (C) 1999-2004 Max Krasnyansky
smc91x.c: v1.1, sep 22 2004 by Nicolas Pitre
eth0: SMC91C11xFD (rev 1) at d080a000 IRQ 25 [nowait]
eth0: Ethernet addr: 52:54:00:12:34:56
mice: PS/2 mouse device common for all mice
TCP cubic registered
ieee80211: 802.11 data/management/control stack, git-1.1.13
ieee80211: Copyright (C) 2004-2005 Intel Corporation
input: AT Raw Set 2 keyboard as /class/input/input0
eth0: link up
input: ImExPS/2 Generic Explorer Mouse as /class/input/input1
IP-Config: Complete:
device=eth0, addr=192.168.7.2, mask=255.255.255.0, gw=192.168.7.1,
host=qemu, domain=, nis-domain=(none),
bootserver=192.168.7.1, rootserver=192.168.7.1, rootpath=
Root-NFS: unknown option: uid=0
Looking up port of RPC 100003/2 on 192.168.7.1
Looking up port of RPC 100005/1 on 192.168.7.1
VFS: Mounted root (nfs filesystem).
Freeing init memory: 100K
init: must be superuser.
Kernel panic - not syncing: Attempted to kill init!

It's looking fairly bright now ;-) All I have to do is figure out why (this has absolutely no real reason) Linux would start up as someone who isn't the superuser
... hmmf..

Weeee !!! I just added an init= option to the 'append' section of Qemu!!! sahweet!!! She's ready to roll ;-)

The option to enable 16-bit UID system calls must be selected as well, otherwise root (0) will get mapped to 0xffffffff (-1 in 2's compliment == -EPERM).

My experiences with Qemu - part I ... was "Building GNU Classpath for the ARM (Cont'd)"

Ok, so it looks like the external USB hard disk idea was not as good as I was hoping. The problem is that the board just has too little RAM !!! (to compile such a package as the GNU Classpath)

What happens in either the NFS case or the USB HD case, is that eventually the swapd and the jikes process enter this vicious cycle, where jikes caches the first half of what it needs to compile, swaps it out, and then caches the second half of what it needs to compile - clearly if it doesn't have 100% of the things it needs to compile in RAM (this occurred even without using -pipe) then it will enter an infinite loop (it would be nice if that was detected by jikes - i think that's CRC32 or something?).

In any event, with the suggestion that my boss Dave gave me, I'm now working on emulating an appropriate kernel, and using the appropriate uclibc-softfloat userspace for the ARM, using Qemu. This should solve all of my compilation woes because I would then be able to have enough actual physical RAM to compile everything natively. I believe that the VersatilePB platform available in Qemu has a limit of 256MB RAM though. That should be enough (I assume).

Aside from the target having a different name, the main other differences between the TS-7xxx boards and the Versatile PB are:

• The Versatile PB uses an ARM926T chip instead of an ARM920T
• The Versatile PB supports an SMC 91c111 ethernet device instead of the ep93xx device.
• The Versatile PB names its serial devices /dev/ttyAMA[0-n] instead of /dev/ttyAM[0-n]

All of the exact details are here:

http://fabrice.bellard.free.fr/qemu/qemu-doc.html#SEC53

Now, a brief overview of the differences and what they will mean.

1. The ARM926T chip vs the ARM920T chip. To quote from the linux kernel help page:
   

   This is a variant of the ARM920. It has slightly different instruction sequences for cache and TLB operations. Curiously, there is no documentation on it at the ARM corporate website [EDIT: There is now].
   
   Say Y if you want support for the ARM926T processor. Otherwise, say N.

   
   I tried compiling for the Versatile PB without ARM926T support and that didn't even compile - it would be nice to have the ARM920T as an option here too. Anyways, that's not really a problem. As long as I can run Qemu with an ARM chip emulated and use an NFS root to compile, that's all that matters.
   
   
2. eth0 is eth0 ... I doubt it matters what hardware is underlying for my purposes.
   
   
3. Some scripts and applications will have to be aware of the difference of platform, if i end up coding scripts and things of the like on the emulator. I just as soon wouldn't, but it could be quite beneficial. In any event, that's not a real issue, it's as simple as replacing a string from my perspective. The cool part about that is that we could end up simulating our hardware, including the EM noise model - cool ;-)
   

I'll keep you posted!

Building GNU Classpath for the ARM (Cont'd ...)

I spontaneously decided to copy over the entire Gentoo stage3 filesystem to my external hard-disk, which is recognized as a general USB storage device under linux. NFS was taking waaaaay too long for this compilation. I had checked everything out with top, under linux, played with the swappiness parameter in /proc/sys/vm, and also attempted to renice the jikes processes' priority to a whopping 17! Non of those had a major effect on the cpu-usage of the jikes process. The highest that I'd seen it was 10% for a whole 2 seconds.

The problem lies with NFS root and the overhead associate not only with RPC, but also the fact that my swap was also on the NFS root, effectively squaring the complexity of the overhead. With my Gentoo stage 3 root filesystem located on a locally attached usb storage device, along with the swap file, the speed of compilation increased dramatically! The jikes process has just started and its already achieved 50% of the cpu time! That's up from an average of maybe 3% with the tweaking I mentioned previously.

I'd better mention this to Dave as well, so that he's not stuck ever repeating my stupid mistake of compiling on an NFS root!