From: Pietro Pugni <pietro.pugni@gmail.com>
To: Mkrtchyan, Tigran <tigran.mkrtchyan@desy.de>
Cc: ik@postgresql-consulting.com, pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: Can't get Dell PE T420 (Perc H710) perform better than a MacMini with PostgreSQL
Date: Thu, 2 Apr 2015 16:25:03 +0200
Message-ID: <C33FBFAF-D442-44FA-B76A-6F525BD5851B@gmail.com> (raw)
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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
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To: pgsql-performance@postgresql.org
Cc: pietro.pugni@gmail.com, tigran.mkrtchyan@desy.de
Subject: Re: Can't get Dell PE T420 (Perc H710) perform better than a MacMini with PostgreSQL
In-Reply-To: <C33FBFAF-D442-44FA-B76A-6F525BD5851B@gmail.com>
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