This could be any one of a number of wierd effects that one sees
from time to time. Rather than speculate, would it be too much
to ask you to run objdump --disassemble on the different versions
of your test program and post the results?
----- Original Message -----
From: "jamal" <hadi@xxxxxxxxxx>
To: <linux-mips@xxxxxxxxxxxxxx>
Cc: <sibyte-users@xxxxxxxxxxxx>
Sent: Friday, May 28, 2004 21:36
Subject: weird sb1250 behavior
>
> found some very strange behavior with sb1250.
> Gcc 3.2.3 with sibyte mods. Running Linux 2.4.21 with whatever
> mods off sibyte.
>
> Testcase:
> sending a large amount of traffic
> -->eth0-->someprocessing-->eth1
>
> given the nature of processing, say i was getting 100Kpps throughput.
> Now i fire a very basic program that has just loops and forever
> sums up two numbers.
>
> ---
> 1 #include <stdlib.h>
> 2
> 3 int main ()
> 4 {
> 5 int a = 1;
> 6 int b = 2;
> 7 int c = 0;
> 8 // int c;
> 9 while (1) {
> 10 c = a + b;
> 11 }
> 12 }
> --------
>
> I see very little drop in throughput - probably around 0.01%.
>
> Now comment line 7 then uncomment line 8. Hallelujah.
> Perfomance drops to about 100pps. Thats about a factor of 1000 down!
>
> Interesting thing is if you add a nop (__asm__ __volatile__("nop");)
> in the second version just before the while loop, we get back the same
> performance as in the earlier version.
> Apologies in advance for attaching objdumps (since there maybe folks who
> dont have access to the sibyte tools)
> 1) while-init-dis is for case 1 where c is initialized
> 2) while-noinit-dis is for case 2 where c is not initialize
> 3) while-nop-dis is for case 3 when you have nop thrown in.
>
>
> cheers,
> jamal
>
>
