Re: [DTrace-devel] [PATCH 1/2] Add a cpuinfos BPF map

[Kris Van Hees <kris.van.hees@oracle.com>]

This is not the way to go about this.  If, in order to implement the cpuinfo_t
argument to sched probes, a regular BPF array map is needed so that cpuinfo
data can be accessed for any given CPU id, then the existing map should be
replaced with the new one, and its use updated to access the new one.  That
way you can also keep the name of the map, etc...

Introducing this new map with exactly the same data, and then hoping to
deprecate the old one later is making things more messy.

On Mon, Mar 31, 2025 at 05:45:00PM -0400, eugene.loh--- via DTrace-devel wrote:
> From: Eugene Loh <eugene.loh@oracle.com>
> 
> The cpuinfo BPF map is a per-CPU map that has CPU information
> on each CPU for that CPU.
> 
> Add a cpuinfos BPF map that allows any CPU to access information
> for any other CPU.
> 
> For now, we retain the older per-CPU map.  If desired, a future
> patch can migrate existing uses of the per-CPU map to the new
> map, decommissioning the old one.  This would include map set up:
> 
> *)  libdtrace/dt_dlibs.c:   DT_BPF_SYMBOL(cpuinfo, DT_IDENT_PTR),
> 
> *)  libdtrace/dt_impl.h:    int dt_cpumap_fd;
> 
> *)  libdtrace/dt_bpf.c:     dtp->dt_cpumap_fd = ...
>     libdtrace/dt_bpf.c:     CREATE_MAP(cpuinfo)
> 
> and map use:
> 
> *)  bpf/get_agg.c
> *)  bpf/get_bvar.c
> *)  libdtrace/dt_cg.c
> *)  libdtrace/dt_prov_lockstat.c
> 
> Signed-off-by: Eugene Loh <eugene.loh@oracle.com>
> ---
>  libdtrace/dt_bpf.c   | 13 +++++++++++++
>  libdtrace/dt_dlibs.c |  1 +
>  libdtrace/dt_impl.h  |  1 +
>  3 files changed, 15 insertions(+)
> 
> diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
> index 6d42a96c7..8da51d6b9 100644
> --- a/libdtrace/dt_bpf.c
> +++ b/libdtrace/dt_bpf.c
> @@ -786,7 +786,20 @@ gmap_create_cpuinfo(dtrace_hdl_t *dtp)
>  	if (dtp->dt_cpumap_fd == -1)
>  		return -1;
>  
> +	dtp->dt_cpusmap_fd = create_gmap(dtp, "cpuinfos",
> +					BPF_MAP_TYPE_HASH,
> +					sizeof(uint32_t),
> +					sizeof(dt_bpf_cpuinfo_t), ncpus);
> +	if (dtp->dt_cpusmap_fd == -1)
> +		return -1;
> +
>  	rc = dt_bpf_map_update(dtp->dt_cpumap_fd, &key, data);
> +
> +	for (i = 0, ci = &conf->cpus[0]; i < ncpus && rc != -1; i++, ci++) {
> +		key = ci->cpu_id;
> +		rc = dt_bpf_map_update(dtp->dt_cpusmap_fd, &key, &data[ci->cpu_id]);
> +	}
> +
>  	dt_free(dtp, data);
>  	if (rc == -1)
>  		return dt_bpf_error(dtp,
> diff --git a/libdtrace/dt_dlibs.c b/libdtrace/dt_dlibs.c
> index 21df22a8a..0f19f3566 100644
> --- a/libdtrace/dt_dlibs.c
> +++ b/libdtrace/dt_dlibs.c
> @@ -61,6 +61,7 @@ static const dt_ident_t		dt_bpf_symbols[] = {
>  	DT_BPF_SYMBOL(agggen, DT_IDENT_PTR),
>  	DT_BPF_SYMBOL(buffers, DT_IDENT_PTR),
>  	DT_BPF_SYMBOL(cpuinfo, DT_IDENT_PTR),
> +	DT_BPF_SYMBOL(cpuinfos, DT_IDENT_PTR),
>  	DT_BPF_SYMBOL(dvars, DT_IDENT_PTR),
>  	DT_BPF_SYMBOL(gvars, DT_IDENT_PTR),
>  	DT_BPF_SYMBOL(lvars, DT_IDENT_PTR),
> diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
> index 68fb8ec53..a5e42801c 100644
> --- a/libdtrace/dt_impl.h
> +++ b/libdtrace/dt_impl.h
> @@ -390,6 +390,7 @@ struct dtrace_hdl {
>  	int dt_aggmap_fd;	/* file descriptor for the 'aggs' BPF map */
>  	int dt_genmap_fd;	/* file descriptor for the 'agggen' BPF map */
>  	int dt_cpumap_fd;	/* file descriptor for the 'cpuinfo' BPF map */
> +	int dt_cpusmap_fd;	/* file descriptor for the 'cpuinfos' BPF map */
>  	int dt_usdt_pridsmap_fd; /* file descriptor for the 'usdt_prids' BPF map */
>  	int dt_usdt_namesmap_fd; /* file descriptor for the 'usdt_names' BPF map */
>  	dtrace_handle_err_f *dt_errhdlr; /* error handler, if any */
> -- 
> 2.43.5
> 
> 
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