Re: Can't get Dell PE T420 (Perc H710) perform better than a MacMini with PostgreSQL

[Pietro Pugni <pietro.pugni@xxxxxxxxx>]

Hi Tigran,

The modern CPUs trying to be too smart.

try to run this code to disable CPUs c-states:

----> setcpulatency.c

#include <stdio.h>
#include <fcntl.h>
#include <stdint.h>

int main(int argc, char **argv) {
  int32_t l;
  int fd;

  if (argc != 2) {
     fprintf(stderr, "Usage: %s <latency in us>\n", argv[0]);
     return 2;
  }

  l = atoi(argv[1]);
  printf("setting latency to %d us\n", l);
  fd = open("/dev/cpu_dma_latency", O_WRONLY);
  if (fd < 0) {
     perror("open /dev/cpu_dma_latency");
     return 1;
  }

  if (write(fd, &l, sizeof(l)) != sizeof(l)) {
     perror("write to /dev/cpu_dma_latency");
     return 1;
  }

  while (1) pause();
}


——>

your C code should be equivalent to the following:

echo 0 > /dev/cpu_dma_latency

Right?

I executed the above command but time execution increase of about 2 seconds over 129seconds (I’ve executed the transaction several times repeating the procedure of restarting db and redoing transaction). With setting echo 1 > /dev/cpu_dma_latency it returns to 129seconds.

you can use i7z (https://code.google.com/p/i7z/) to see the percentage of CPU power to be used.

I’ve installed i7z-GUI but it reports the following and crashes with segmentation fault (T420 has Intel Xeon, not i-series):

i7z DEBUG: i7z version: svn-r77-(20-Nov-2011)

i7z DEBUG: Found Intel Processor

i7z DEBUG:    Stepping 4

i7z DEBUG:    Model e

i7z DEBUG:    Family 6

i7z DEBUG:    Processor Type 0

i7z DEBUG:    Extended Model 3

i7z DEBUG: msr = Model Specific Register

i7z DEBUG: detected a newer model of ivy bridge processor

i7z DEBUG: my coder doesn't know about it, can you send the following info to him?

i7z DEBUG: model e, extended model 3, proc_family 6

i7z DEBUG: msr device files DONOT exist, trying out a makedev script

i7z DEBUG: modprobbing for msr

[1]+  Segmentation fault      (core dumped) i7z_GUI

Changing CPU from C1 to C0 takes quite some time and for DB workload not optimal (if you need a
high throughout and any given moment).

I see ~65% boost when run './setcpulatency 0'.

Tigran.

With “takes quite some time” you mean that it will take some time to take effect?

Thank you a lot for your help.

Best regards,

 Pietro