On Mon, Jun 1, 2020 at 7:08 PM Carlos O'Donell <carlos@redhat.com> wrote:
>
> On Mon, Jun 1, 2020 at 6:44 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > Tunables are designed to pass info from user to glibc, not the other
> > way around.  When __libc_main is called, init_cacheinfo is never
> > called.  I can call init_cacheinfo from __libc_main.  But there is no
> > interface to update min and max values from init_cacheinfo.  I don't
> > think --list-tunables will work here without changes to tunables.
>
> You have a dynamic threshold.
>
> You have to tell the user what that minimum is, otherwise they can't
> use the tunable reliably.
>
> This is the first instance of a min/max that is dynamically determined.
>
> You must fetch the cache info ahead of the tunable initialization, that
> is you must call init_cacheinfo before __init_tunables.
>
> You can initialize the tunable data dynamically like this:
>
> /* Dynamically set the min and max of glibc.foo.bar.  */
> tunable_id_t id = TUNABLE_ENUM_NAME (glibc, foo, bar);
> tunable_list[id].type.min = lowval;
> tunable_list[id].type.max = highval;
>
> We do something similar for maybe_enable_malloc_check.
>
> Then once the tunables are parsed, and the cpu features are loaded
> you can print the tunables, and the printed tunables will have meaningful
> min and max values.
>
> If you have circular dependency, then you must process the cpu features
> first without reading from the tunables, then allow the tunables to be
> initialized from the system, *then* process the tunables to alter the existing
> cpu feature settings.
>

How about this?  I got

[hjl@gnu-cfl-2 build-x86_64-linux]$ ./elf/ld.so ./libc.so --list-tunables
tunables:
  glibc.elision.skip_lock_after_retries: 0x3 (min: 0x80000000, max: 0x7fffffff)
  glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.malloc.perturb: 0x0 (min: 0x0, max: 0xff)
  glibc.cpu.x86_shared_cache_size: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.elision.tries: 0x3 (min: 0x80000000, max: 0x7fffffff)
  glibc.elision.enable: 0x0 (min: 0x0, max: 0x1)
  glibc.cpu.x86_rep_movsb_threshold: 0x1000 (min: 0x100, max:
0xffffffffffffffff)
  glibc.malloc.mxfast: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.elision.skip_lock_busy: 0x3 (min: 0x80000000, max: 0x7fffffff)
  glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.cpu.x86_rep_stosb_threshold: 0x800 (min: 0x0, max: 0xffffffffffffffff)
  glibc.cpu.x86_non_temporal_threshold: 0x600000 (min: 0x0, max:
0xffffffffffffffff)
  glibc.cpu.x86_shstk:
  glibc.cpu.hwcap_mask: 0x6 (min: 0x0, max: 0xffffffffffffffff)
  glibc.malloc.mmap_max: 0x0 (min: 0x80000000, max: 0x7fffffff)
  glibc.elision.skip_trylock_internal_abort: 0x3 (min: 0x80000000,
max: 0x7fffffff)
  glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.cpu.x86_ibt:
  glibc.cpu.hwcaps:
  glibc.elision.skip_lock_internal_abort: 0x3 (min: 0x80000000, max: 0x7fffffff)
  glibc.malloc.arena_max: 0x0 (min: 0x1, max: 0xffffffffffffffff)
  glibc.malloc.mmap_threshold: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.cpu.x86_data_cache_size: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.malloc.tcache_count: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.malloc.arena_test: 0x0 (min: 0x1, max: 0xffffffffffffffff)
  glibc.pthread.mutex_spin_count: 0x64 (min: 0x0, max: 0x7fff)
  glibc.malloc.tcache_max: 0x0 (min: 0x0, max: 0xffffffffffffffff)
  glibc.malloc.check: 0x0 (min: 0x0, max: 0x3)
[hjl@gnu-cfl-2 build-x86_64-linux]$

-- 
H.J.