what cflag/march to use for intel core duo l2400?

what cflag/march to use for intel core duo l2400?

[George Nychis]

Hi,

I was wondering what march to specify in my cflags for the Intel Core 
Duo L2400 processor.  The gentoo-wiki says that the safe cflag is 
prescott, but I figured I would ask here to find the optimal for this 
processor, or if the prescott is truly the safest/optimal.

Here is my /proc/cpuinfo for it:
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 14
model name	: Genuine Intel(R) CPU           L2400  @ 1.66GHz
stepping	: 8
cpu MHz		: 1662.571
cache size	: 2048 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 2
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov 
pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx pni monitor vmx 
est tm2 xtpr
bogomips	: 3331.72

processor	: 1
vendor_id	: GenuineIntel
cpu family	: 6
model		: 14
model name	: Genuine Intel(R) CPU           L2400  @ 1.66GHz
stepping	: 8
cpu MHz		: 1662.571
cache size	: 2048 KB
physical id	: 0
siblings	: 2
core id		: 1
cpu cores	: 2
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov 
pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx pni monitor vmx 
est tm2 xtpr
bogomips	: 3325.15

- George

Re: what cflag/march to use for intel core duo l2400?

[Tim Prince]

George Nychis wrote:
> Hi,
> 
> I was wondering what march to specify in my cflags for the Intel Core 
> Duo L2400 processor.  The gentoo-wiki says that the safe cflag is 
> prescott, but I figured I would ask here to find the optimal for this 
> processor, or if the prescott is truly the safest/optimal.
The wiki might be right, if you are using the same gcc version they have 
in mind.  How are we to know?  Might there a conflict between safety and 
optimality?
Do you disqualify gcc-4.2 on grounds of safety?  Surely, it would often 
generate better code, and avoid the question of what -march option to 
choose.

Re: what cflag/march to use for intel core duo l2400?

[George Nychis]

Tim Prince wrote:
> George Nychis wrote:
> 
>> Hi,
>>
>> I was wondering what march to specify in my cflags for the Intel Core 
>> Duo L2400 processor.  The gentoo-wiki says that the safe cflag is 
>> prescott, but I figured I would ask here to find the optimal for this 
>> processor, or if the prescott is truly the safest/optimal.
> 
> The wiki might be right, if you are using the same gcc version they have 
> in mind.  How are we to know?  Might there a conflict between safety and 
> optimality?
> Do you disqualify gcc-4.2 on grounds of safety?  Surely, it would often 
> generate better code, and avoid the question of what -march option to 
> choose.
> 

I'd prefer sticking to gcc-4.1

Check out this response i got on the lkml about the architecture:
 >> My guess is the "Pentium-4/Celeron(P4-based)/Pentium-4 M/Xeon" >family,
 >> but maybe someone has a different opinion or can support it.
 >>
 >> Here is the /proc/cpuinfo:
 >> processor       : 0
 >> vendor_id       : GenuineIntel
 >> cpu family      : 6
 >> model           : 14
 >
 >[snip]
 >
 >"Pentium-4/Celeron(P4-based)/Pentium-4 M/Xeon" are all family 15, not 
 >family 6.
 >
 >I have a Pentium M, it's family 6 model 13. Also, AFAIK the Intel Core
 >is based on the Pentium M (which in turn is based on Pentium III). So,
 >my personal best guess would be to choose "Pentium M".
 >
 >Unfortunately, I don't have one of these (Intel Core) at this point,
 >so I can't test it myself...

So, this person has a pentium m, and /proc/cpu info says his processor 
belongs to family 6... as you can see, mine also belongs to family 6... 
so even though the wiki stages march=prescott, what do you guys think?

- George

Re: what cflag/march to use for intel core duo l2400?

[Tim Prince]

George Nychis wrote:
> 
> 

> I'd prefer sticking to gcc-4.1
> 
> So, this person has a pentium m, and /proc/cpu info says his processor 
> belongs to family 6... as you can see, mine also belongs to family 6... 
> so even though the wiki stages march=prescott, what do you guys think?
> 
-march=pentium-m prefers x87 over sse scalar code, because pentium-m can 
decode sse at only half the rate of x87. You should see the speed 
advantage clearly on pentium-m, presumably not on Core Duo.