Re: [Xen-devel] xen-2.0 20040923 and previous: rpm crash in xenU

[Peri Hankey <mpah@xxxxxxxxxxxxxx>]

Thanks for sending the test - one point of interest is that my 
/proc/cpuinfo doesn't match your expectations - presumably an AMD 
Athlon(tm) XP 2400+ is running at 2400MHz. The main point however is 
that the results are indeed different in the two domains:
----------------  xen0 ------------------------

[me@xen0 testing]$ ./time-test
find_cpu_speed: error parsing /proc/cpuinfo for cpu MHz. Assume 2400 
MhzCPU speed = 2400 MHz
...........................................................................................................
...........................................................................................................
... (lots of dots)

[me@xen0 testing]$ cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 8
model name      : AMD Athlon(tm) XP 2400+
stepping        : 1
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : yes
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu msr pae mce cx8 apic sep mca cmov pat pse36 mmx 
sse syscall mmxext 3dnowext 3dnow
bogomips        : 4010.80

----------------  xenU ------------------------

[me@xenU testing]$ ./time-test
find_cpu_speed: error parsing /proc/cpuinfo for cpu MHz. Assume 2400 
MhzCPU speed = 2400 MHz
nanosleep(20000us): gtod 0
.nanosleep(20000us): gtod 0
.nanosleep(20000us): gtod 0
.nanosleep(20000us): gtod 0
.nanosleep(20000us): gtod 0
.nanosleep(20000us): gtod 0
.nanosleep(20000us): gtod 0
.nanosleep(20000us): gtod 0
... (lots of gtod 0s)

[me@xenU testing]$ cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 8
model name      : AMD Athlon(tm) XP 2400+
stepping        : 1
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : yes
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu msr pae mce cx8 apic sep mca cmov pat pse36 mmx 
sse syscall mmxext 3dnowext 3dnow
bogomips        : 3263.69

I hope this will help nail it down - I notice also that the bogomips 
measure is different. No time for more just now - but I have a more 
general question about lvm2 cows and snapshots, which I will put in a 
separate message. 'A snapshot is not a cow' as the liftman said to Babar 
the Elephant. In fact the problem is that snapshots hold on to each 
other's tails.
Thanks for your help.
Peri


Ian Pratt wrote:

> > I have previously mentioned a floating point exception in rpm which 
> > seemed at one point to be connected with block-device handling in xenU 
> > systems, as both problems occurred at the same time. As I now get only 
> > the rpm floating point exception (sporadically), I have examined it further:
> > gettimeofday({1096021305, 741150}, NULL) = 0
> > nanosleep({0, 20000000}, {1076798912, 1075195904}) = 0
> > gettimeofday({1096021305, 741150}, NULL) = 0
> > --- SIGFPE (Floating point exception) @ 0 (0) ---
> > +++ killed by SIGFPE +++
> >
> >    
> I've tried hard to reproduce this but failed. It might be worth
> having a look at the rpm source to check that the nanosleep is
> wrapped in a while loop, and where the presumed division by zero
> is really coming from.
>
> Since the strace prints the arguments that gettimeofday is passed
> rather than returns, we can't really tell from the trace what
> gettimeofday is actually returning. If there's a following call
> in the trace using the same struct we can probably deduce it.
>
> I've appended the test program I've used to debug this and other
> time issues. You might want to run it on your system just to
> check.
>
> Thanks,
> Ian
>
>
> #include <stdlib.h>
> #include <stdio.h>
> #include <sys/time.h>
> #include <time.h>
>
> /**************************************************************************/
>
>
> /* rpcc: get full 64-bit Pentium TSC value */
> static __inline__ unsigned long long int rpcc(void) 
> {
>    unsigned int __h, __l;
>    __asm__ __volatile__ ("rdtsc" :"=a" (__l), "=d" (__h));
>    return (((unsigned long long)__h) << 32) + __l;
> }
>
>
> /*
> * find_cpu_speed:
> *   Interrogates /proc/cpuinfo for the processor clock speed.
> * 
> *   Returns: speed of processor in MHz, rounded down to nearest whole MHz.
> */
> #define MAX_LINE_LEN 50
> int find_cpu_speed(void)
> {
>    FILE *f;
>    char s[MAX_LINE_LEN], *a, *b;
>    int mhz = 2400;
>
>    if ( (f = fopen("/proc/cpuinfo", "r")) == NULL ) goto out;
>
>    while ( fgets(s, MAX_LINE_LEN, f) )
>    {
>        if ( strstr(s, "cpu MHz") )
>        {
>            /* Find the start of the speed value, and stop at the dec point. */
>            if ( !(a=strpbrk(s,"0123456789")) || !(b=strpbrk(a,".")) ) break;
>            *b = '\0';
>            fclose(f);
>            return(atoi(a));
>        }
>    }
>
> out:    
>    fprintf(stderr, "find_cpu_speed: error parsing /proc/cpuinfo for cpu MHz. Assume %d Mhz",mhz);
>    return mhz;
>
> }
>
> int mhz;
>
> int looper (int N)
> {
>    int i,a=12345;
>    for(i=0;i<N;i++)
>         a*=a;
>    return a;
> }
>
>
> main()
> {
>    int stride;
>    unsigned long long start=0,stop=0, last=0, now, gt_firsteventtime;
>    unsigned long long xnow, xlast, skip;
>    unsigned long long firsteventtime=0, lasteventtime, lastfirsteventtime = 0;
>    struct timeval a,b;
>    int count=0, okcount=0;
>
>    /* Required in order to print intermediate results at fixed period. */
>    mhz = find_cpu_speed();
>    printf("CPU speed = %d MHz\n", mhz);
>
>
> #define SLEEP (20*1000)
>
>    while(1)
>    {
>         struct timespec z = { 0, SLEEP*1000 };
>
>         gettimeofday(&a, NULL);
>         while(nanosleep(&z,&z)); // loop until success
>         gettimeofday(&b, NULL);
>
>         last = (((long long)a.tv_sec) * 1000000) + a.tv_usec;
>         now  = (((long long)b.tv_sec) * 1000000) + b.tv_usec;
>
>         if ( now - last < SLEEP )
>         {
>             printf("nanosleep(%dus): gtod %d\n",
>                    SLEEP, now-last );
>         }
>
>         fprintf(stderr,".");  
>    }
>
>
>
>    gettimeofday(&a, NULL);
>    xlast = rpcc();
>    last = (((long long)a.tv_sec) * 1000000) + a.tv_usec;
>    while(1)
>    {
>         struct timespec z = { 0, SLEEP*1000 };
>
>         while(nanosleep(&z,&z)); // loop until success
>         gettimeofday(&a, NULL);
>         xnow = rpcc();
>        now = (((long long)a.tv_sec) * 1000000) + a.tv_usec;
>
>         if ( now - last < SLEEP )
>         {
>             printf("nanosleep(%d): gtod %d  rpcc %d\n",
>                    SLEEP, now-last, (xnow-xlast)/mhz );
>         }
>
>         last = now;
>         xlast = xnow;
>
>         if((count++ % 64) == 0)fprintf(stderr,".");
>    }
>
>
>    start = rpcc();
>    while(1)
>    {
>         gettimeofday(&a, NULL);
>         xnow = rpcc();
>
>         if(xnow < xlast)
>             printf("** %lld %lld **\n", xnow, xlast);
>
>        now = (((long long)a.tv_sec) * 1000000) + a.tv_usec;
>
>         if(now<last)
>         {
>             printf("backwards!\n");
>             exit(-1);
>         }
>
> 	if(now==last) 
> 	{
>             count++;
>             lasteventtime = rpcc();
> 	    if( firsteventtime == 0 ) 
> 	    {
>                 firsteventtime = lasteventtime;
>                 gt_firsteventtime = now;
>                 skip = (xnow-xlast)/mhz;
>             }
>
>         }
>
>         if(now>last)
>         {
>             if(count>5)
>             {
>                 printf("[%lld.%lld %lld] duplicates= % 5d (% 5lldus)\t prev OK= % 
> 6d\t fe %lldus (d=%lldus) skip = %lld\n",
>                        gt_firsteventtime/1000000,gt_firsteventtime%1000000,
>                        firsteventtime,
>                        count, (lasteventtime-firsteventtime)/mhz,
>                        okcount,(firsteventtime-start)/mhz,
>                        (firsteventtime-lastfirsteventtime)/mhz,
>                        skip);
>                 okcount = 0;
>                 lastfirsteventtime = firsteventtime;
>             }
>             count = 0;
>             firsteventtime = 0;
>             okcount++;
>         }
>         
>         last = now;
>         xlast = xnow;
>    }
>
>   
> #if 0
>    while(1)
>    {
> int i;
>        gettimeofday(&a, NULL);
> for(i=0;i<10000;i++);
>         gettimeofday(&b, NULL);
>        start = (((long long)a.tv_sec) * 1000000) + a.tv_usec;
>         stop  = (((long long)b.tv_sec) * 1000000) + b.tv_usec;
>
>        if(1||stop<start) printf("crap : %ld\n",stop-start);
>    }
>         
>    while(1)
>    {
>         gettimeofday(&a, NULL);
>         start = (((long long)a.tv_sec) * 1000000) + a.tv_usec;
>
>         looper(1000000);
>
>         gettimeofday(&a, NULL);
>         stop = (((long long)a.tv_sec) * 1000000) + a.tv_usec;
>
>         printf("%ld\n",stop-start);
>
>    }
>
>
> #endif
>
>
>
>
> }
>
>
>  


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