On Wed, Dec 18, 2019 at 03:23:04PM +0100, Paul Chaignon wrote:
> Currently, userspace programs have to update the values of all CPUs at
> once when updating per-cpu maps. This limitation prevents the update of
> a single CPU's value without the risk of missing concurrent updates on
> other CPU's values.
>
> This patch allows userspace to update the value of a specific CPU in
> per-cpu maps. The CPU whose value should be updated is encoded in the
> 32 upper-bits of the flags argument, as follows. The new BPF_CPU flag
> can be combined with existing flags.
In general makes sense. Could you elaborate more on concrete issue?
> bpf_map_update_elem(..., cpuid << 32 | BPF_CPU)
>
> Signed-off-by: Paul Chaignon <paul.chaignon@xxxxxxxxxx>
> ---
> include/uapi/linux/bpf.h | 4 +++
> kernel/bpf/arraymap.c | 19 ++++++++-----
> kernel/bpf/hashtab.c | 49 ++++++++++++++++++++--------------
> kernel/bpf/local_storage.c | 16 +++++++----
> kernel/bpf/syscall.c | 17 +++++++++---
> tools/include/uapi/linux/bpf.h | 4 +++
> 6 files changed, 74 insertions(+), 35 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index dbbcf0b02970..2efb17d2c77a 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -316,6 +316,10 @@ enum bpf_attach_type {
> #define BPF_NOEXIST 1 /* create new element if it didn't exist */
> #define BPF_EXIST 2 /* update existing element */
> #define BPF_F_LOCK 4 /* spin_lock-ed map_lookup/map_update */
> +#define BPF_CPU 8 /* single-cpu update for per-cpu maps */
BPF_F_CPU would be more consistent with the rest of flags.
Can BPF_F_CURRENT_CPU be supported as well?
And for consistency support this flag in map_lookup_elem too?
> +
> +/* CPU mask for single-cpu updates */
> +#define BPF_CPU_MASK 0xFFFFFFFF00000000ULL
what is the reason to expose this in uapi?
> /* flags for BPF_MAP_CREATE command */
> #define BPF_F_NO_PREALLOC (1U << 0)
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index f0d19bbb9211..a96e94696819 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -302,7 +302,8 @@ static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
> u32 index = *(u32 *)key;
> char *val;
>
> - if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST))
> + if (unlikely((map_flags & ~BPF_CPU_MASK & ~BPF_F_LOCK &
> + ~BPF_CPU) > BPF_EXIST))
that reads odd.
More traditional would be ~ (A | B | C)
