Le 30/08/2024 à 18:26, Uladzislau Rezki a écrit :
At least in my case, HW, i do not see that atomic_long_add_return() is a
top when it comes to CPU cycles. Below one is the hottest instead:
static bool
is_vn_id_valid(unsigned int node_id)
{
if (node_id < nr_vmap_nodes)
return true;
return false;
}
access to "nr_vmap_nodes" which is read-only and globally defined:
static __read_mostly unsigned int nr_vmap_nodes = 1;
Any thoughts?
--
Uladzislau Rezki
Hi,
unrelated to your use case, but something that coud easily save a few
cycles on some system, IMHO.
Maybe:
#if NR_CPUS > 1
static __read_mostly unsigned int nr_vmap_nodes = 1;
static __read_mostly unsigned int vmap_zone_size = 1;
#else
#define nr_vmap_nodes 1
#define vmap_zone_size 1
#endif
So that the compiler can do a better job because some loops can be
optimized away and there is no need to access some memory to get theses
values.
Not sure if such a use case can exist or is of any interest.
This is valide because of [1] and the #ifdef around the
num_possible_cpus() declaration [2, 3].
Just my 2c.
CJ
[1]: https://elixir.bootlin.com/linux/v6.11-rc5/source/mm/vmalloc.c#L5026
[2]:
https://elixir.bootlin.com/linux/v6.11-rc5/source/include/linux/cpumask.h#L1083
[3]:
https://elixir.bootlin.com/linux/v6.11-rc5/source/include/linux/cpumask.h#L1136
