Re: Very slow transfers to/from micro SD card on a RPi B+

[Stephan <stephanwib%googlemail.com@localhost>]

Nobody having an idea about DIRHASH? I´ve also seen that tmpfs has the
same regression.


I corrected 2 minor flaws in my tool, if it´s useful to somebody:


------8<---------------------------------

#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/time.h>

int main(int argc, char **argv) {
  struct timeval tv_start, tv_finish;
  unsigned long duration;
  int i;
  char filename[16];

  if (argc < 2) { printf("Usage: %s <count>\n", argv[0]); exit(1); }
  int howmany = atoi(argv[1]);

  for (i = 0; i < howmany; i++)
  {
    snprintf(filename, sizeof(filename), "%d", i);
    gettimeofday(&tv_start, NULL);
    int fd = open(filename, O_CREAT);
    gettimeofday(&tv_finish, NULL);
    close(fd);
    duration = (tv_finish.tv_sec * 1000000 + tv_finish.tv_usec) -
(tv_start.tv_sec * 1000000 + tv_start.tv_usec);
    printf("Duration: %lu\n", duration);
  }

  return 0;
}

2015-08-20 18:16 GMT+02:00 Stephan <stephanwib%googlemail.com@localhost>:
> 2015-08-19 15:51 GMT+02:00 Thor Lancelot Simon <tls%panix.com@localhost>:
>> We should be shipping with DIRHASH turned on.
>
>
> That´s it - top speed!
>
> /root/test/files> time seq 1 30000|xargs touch
>     1.05s real     0.03s user     0.84s system
>
> Is DIRHASH still considered experimental? It fixes one of NetBSD´s
> most annoying shortcomings.
>
> FreeBSD received dynamic memory allocation for DIRHASH which might be
> even better.
>
>
>
> (re-sending this as my editor intermittently distributes HTML mails)
>
>
>>
>> On Tue, Aug 18, 2015 at 04:19:57PM +0000, Michael van Elst wrote:
>>> stephanwib%googlemail.com@localhost (Stephan) writes:
>>>
>>> >This is from an amd64 server box with an aac raid controller.
>>>
>>> >/root/test/files> time seq 1 10000|xargs touch
>>> >    3.10s real     0.01s user     3.07s system
>>> >/root/test/files> rm *
>>> >/root/test/files> time seq 1 20000|xargs touch
>>> >    9.88s real     0.01s user     8.51s system
>>> >/root/test/files> rm *
>>> >/root/test/files> time seq 1 30000|xargs touch
>>> >   23.45s real     0.04s user    20.41s system
>>> >/root/test/files> time seq 1 40000|xargs touch
>>> >   43.35s real     0.05s user    38.32s system
>>>
>>> >That is clearly not linear.
>>>
>>> Each lookup is linear (unless you use DIRHASH), so the total
>>> time goes with n^2.
>>>
>>> --
>>> --
>>>                                 Michael van Elst
>>> Internet: mlelstv%serpens.de@localhost
>>>                                 "A potential Snark may lurk in every tree."
>>
>> --
>>   Thor Lancelot Simon                                        tls%panix.com@localhost
>>
>>   "We cannot usually in social life pursue a single value or a single moral
>>    aim, untroubled by the need to compromise with others."      - H.L.A. Hart