RFC: ABI support for special memory area

[H.J. Lu]

On Mon, Mar 6, 2017 at 5:25 AM, Suprateeka R Hegde
<hegdesmailbox@gmail.com> wrote:
> On 04-Mar-2017 07:37 AM, Carlos O'Donell wrote:
>>
>> On 03/03/2017 11:00 AM, H.J. Lu wrote:
>>>
>>> __gnu_mbind_setup is called from ld.so.  Since there is only one ld.so,
>>> it needs to know what to pass to __gnu_mbind_setup.  Not all arguments
>>> have to be used by all implementations nor all memory types.
>>
>>
>> I think what Supra is suggesting is a pointer-to-implementation interface
>> which would allow ld.so to pass completely different arguments to the
>> library depending on what kind of memory is being defined by the sh_info
>> value. It avoids needing to encode all the types in the API, and just
>> uses an incomplete pointer to the type.
>
>
> Thats absolutely right.
>
> However, I am not suggesting one is better over the other. I just want to
> get clarity on how the code looks like for different implementations.
>
> On 03-Mar-2017 09:30 PM, H.J. Lu wrote:
>>
>> __gnu_mbind_setup is called from ld.so.  Since there is only one ld.so,
>> it needs to know what to pass to __gnu_mbind_setup.
>
>
> So I want to know what is that ONE-FIXED-FORM of __gnu_mbind_setup being
> called by ld.so.
>
>>  Not all arguments
>> have to be used by all implementations nor all memory types.
>
>
> I think I am still not getting this. Really sorry for that. Would it be
> possible for you to write a small pseudo code that depicts how this design
> looks like for different implementations?
>

For my usage, I only want to know memory type, address and its size:

#define _GNU_SOURCE
#include <unistd.h>
#include <errno.h>
#include <stdint.h>
#include <cpuid.h>
#include <numa.h>
#include <numaif.h>
#include <mbind.h>

#ifdef LIBMBIND_DEBUG
#include <stdio.h>
#endif

/* High-Bandwidth Memory node mask.  */
static struct bitmask *hbw_node_mask;

/* Initialize High-Bandwidth Memory node mask.  This must be called before
   __gnu_mbind_setup.  */
static void
__attribute__ ((used, constructor))
init_node_mask (void)
{
  if (__get_cpuid_max (0, 0) == 0)
    return;

  /* Check if vendor is Intel.  */
  uint32_t eax, ebx, ecx, edx;
  __cpuid (0, eax, ebx, ecx, edx);
  if (!(ebx == 0x756e6547 && ecx == 0x6c65746e && edx == 0x49656e69))
    return;

  /* Get family and model.  */
  uint32_t model;
  uint32_t family;
  __cpuid (1, eax, ebx, ecx, edx);
  family = (eax >> 8) & 0x0f;
  if (family != 0x6)
    return;
  model = (eax >> 4) & 0x0f;
  model += (eax >> 12) & 0xf0;

  /* Check for KNL and KNM.  */
  switch (model)
    {
    default:
      return;

    case 0x57: /* Knights Landing.  */
    case 0x85: /* Knights Mill.  */
      break;
    }

  /* Check if NUMA configuration is supported.  */
  int nodes_num = numa_num_configured_nodes ();
  if (nodes_num < 2)
    return;

  /* Get MCDRAM NUMA nodes.  */
  struct bitmask *node_mask = numa_allocate_nodemask ();
  struct bitmask *node_cpu = numa_allocate_cpumask ();

  int i;
  for (i = 0; i < nodes_num; i++)
    {
      numa_node_to_cpus (i, node_cpu);
      /* NUMA node without CPU is MCDRAM node.  */
      if (numa_bitmask_weight (node_cpu) == 0)
numa_bitmask_setbit (node_mask, i);
    }

  if (numa_bitmask_weight (node_mask) != 0)
    {
      /* On Knights Landing and Knights Mill, MCDRAM is High-Bandwidth
Memory.  */
      hbw_node_mask = node_mask;
    }
  else
    numa_bitmask_free (node_mask);
  numa_bitmask_free (node_cpu);
}

/* Support all different memory types.  */

static int
mbind_setup (unsigned int type, void *addr, size_t length,
    unsigned int mode, unsigned int flags)
{
  int err = ENXIO;

  switch (type)
    {
    default:
#ifdef LIBMBIND_DEBUG
      printf ("Unsupported mbind type %d: from %p of size %p\n",
     type, addr, length);
#endif
      return EINVAL;

    case GNU_MBIND_HBW:
      if (hbw_node_mask)
err = mbind (addr, length, mode, hbw_node_mask->maskp,
    hbw_node_mask->size, flags);
      break;
    }

  if (err < 0)
    err = errno;

#ifdef LIBMBIND_DEBUG
  printf ("Mbind type %d: from %p of size %p\n", type, addr, length);
#endif

  return err;
}

int
__gnu_mbind_setup (unsigned int type, void *addr, size_t length)
{
  return mbind_setup (type, addr, length, MPOL_BIND, MPOL_MF_MOVE);
}

If other memory types need additional information, they can be
passed to __gnu_mbind_setup.  We just need to know what
information is needed.


-- 
H.J.