[DTrace-devel] [PATCH 7/8] rawfbt: performance improvements

[Eugene Loh]

Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
Honestly, I hardly looked at this one.  It looks much like the preceding 
patch, and any sins, if any, will presumably be uncovered in the next patch.

On 3/7/25 16:34, Kris Van Hees via DTrace-devel wrote:
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
>   libdtrace/dt_prov_rawfbt.c | 223 +++++++++++++++++++++++++------------
>   1 file changed, 151 insertions(+), 72 deletions(-)
>
> diff --git a/libdtrace/dt_prov_rawfbt.c b/libdtrace/dt_prov_rawfbt.c
> index 62f2f4f0..52152655 100644
> --- a/libdtrace/dt_prov_rawfbt.c
> +++ b/libdtrace/dt_prov_rawfbt.c
> @@ -44,10 +44,8 @@
>   #include "dt_pt_regs.h"
>   
>   static const char		prvname[] = "rawfbt";
> -static const char		modname[] = "vmlinux";
>   
>   #define KPROBE_EVENTS		TRACEFS "kprobe_events"
> -#define PROBE_LIST		TRACEFS "available_filter_functions"
>   
>   #define FBT_GROUP_FMT		GROUP_FMT "_%s"
>   #define FBT_GROUP_DATA		GROUP_DATA, prp->desc->prb
> @@ -61,98 +59,178 @@ static const dtrace_pattr_t	pattr = {
>   };
>   
>   /*
> - * Scan the PROBE_LIST file and add entry and return probes for every function
> - * that is listed.
> + * Create the rawfbt provider.
>    */
>   static int populate(dtrace_hdl_t *dtp)
>   {
>   	dt_provider_t		*prv;
> -	FILE			*f;
> -	char			*buf = NULL;
> -	size_t			len = 0;
> -	size_t			n = 0;
> -	dtrace_syminfo_t	sip;
> -	dtrace_probedesc_t	pd;
>   
>   	prv = dt_provider_create(dtp, prvname, &dt_rawfbt, &pattr, NULL);
>   	if (prv == NULL)
>   		return -1;			/* errno already set */
>   
> -	f = fopen(PROBE_LIST, "r");
> -	if (f == NULL)
> +	return 0;
> +}
> +
> +/* Create a probe (if it does not exist yet). */
> +static int provide_probe(dtrace_hdl_t *dtp, const dtrace_probedesc_t *pdp)
> +{
> +	dt_provider_t	*prv = dt_provider_lookup(dtp, pdp->prv);
> +
> +	if (prv == NULL)
>   		return 0;
> +	if (dt_probe_lookup(dtp, pdp) != NULL)
> +		return 0;
> +#ifdef DEBUG_FBT
> +	if (dt_tp_probe_insert(dtp, prv, pdp->prv, pdp->mod, pdp->fun, pdp->prb)) {
> +		fprintf(stderr, "%s(..., PROVIDE %s:%s:%s:%s) - ...\n", __func__, pdp->prv, pdp->mod, pdp->fun, pdp->prb);
> +		return 1;
> +	}
> +#else
> +	if (dt_tp_probe_insert(dtp, prv, pdp->prv, pdp->mod, pdp->fun, pdp->prb))
> +		return 1;
> +#endif
>   
> -	while (getline(&buf, &len, f) >= 0) {
> -		char		*p;
> -		const char	*mod = modname;
> -		dt_probe_t	*prp;
> +	return 0;
> +}
>   
> -		/*
> -		 * Here buf is either "funcname\n" or "funcname [modname]\n".
> -		 * The last line may not have a linefeed.
> -		 */
> -		p = strchr(buf, '\n');
> -		if (p) {
> -			*p = '\0';
> -			if (p > buf && *(--p) == ']')
> -				*p = '\0';
> +/*
> + * Try to provide probes for the given probe description.  The caller ensures
> + * that the provider name in probe desxcription (if any) is a match for this
> + * provider.  When this is called, we already know that this provider matches
> + * the provider component of the probe specification.
> + */
> +#define FBT_ENTRY	1
> +#define FBT_RETURN	2
> +
> +static int provide(dtrace_hdl_t *dtp, const dtrace_probedesc_t *pdp)
> +{
> +	int			n = 0;
> +	int			prb = 0;
> +	dt_module_t		*dmp = NULL;
> +	dt_symbol_t		*sym = NULL;
> +	dt_htab_next_t		*it = NULL;
> +	dtrace_probedesc_t	pd;
> +
> +	dt_modsym_mark_traceable(dtp);
> +
> +	/*
> +	 * Nothing to do if a probe name is specified and cannot match 'entry'
> +	 * or 'return'.
> +	 */
> +	if (dt_gmatch("entry", pdp->prb))
> +		prb |= FBT_ENTRY;
> +	if (dt_gmatch("return", pdp->prb))
> +		prb |= FBT_RETURN;
> +	if (prb == 0)
> +		return 0;
> +
> +	/*
> +	 * If we have an explicit module name, check it.  If not found, we can
> +	 * ignore this request.
> +	 */
> +	if (pdp->mod[0] != '\0' && strchr(pdp->mod, '*') == NULL) {
> +		dmp = dt_module_lookup_by_name(dtp, pdp->mod);
> +		if (dmp == NULL)
> +			return 0;
> +	}
> +
> +	/*
> +	 * If we have an explicit function name, we start with a basic symbol
> +	 * name lookup.
> +	 */
> +	if (pdp->fun[0] != '\0' && strchr(pdp->fun, '*') == NULL) {
> +		/* If we have a module, use it. */
> +		if (dmp != NULL) {
> +			sym = dt_module_symbol_by_name(dtp, dmp, pdp->fun);
> +			if (sym == NULL)
> +				return 0;
> +			if (!dt_symbol_traceable(sym))
> +				return 0;
> +
> +			pd.id = DTRACE_IDNONE;
> +			pd.prv = pdp->prv;
> +			pd.mod = dmp->dm_name;
> +			pd.fun = pdp->fun;
> +
> +			if (prb & FBT_ENTRY) {
> +				pd.prb = "entry";
> +				n += provide_probe(dtp, &pd);
> +			}
> +			if (prb & FBT_RETURN) {
> +				pd.prb = "return";
> +				n += provide_probe(dtp, &pd);
> +			}
> +
> +			return n;
>   		}
>   
> -		/*
> -		 * Now buf is either "funcname" or "funcname [modname".  If
> -		 * there is no module name provided, we will use the default.
> -		 */
> -		p = strchr(buf, ' ');
> -		if (p) {
> -			*p++ = '\0';
> -			if (*p == '[')
> -				p++;
> +		sym = dt_symbol_by_name(dtp, pdp->fun);
> +		while (sym != NULL) {
> +			const char	*mod = dt_symbol_module(sym)->dm_name;
> +
> +			if (dt_symbol_traceable(sym) &&
> +			    dt_gmatch(mod, pdp->mod)) {
> +				pd.id = DTRACE_IDNONE;
> +				pd.prv = pdp->prv;
> +				pd.mod = mod;
> +				pd.fun = pdp->fun;
> +
> +				if (prb & FBT_ENTRY) {
> +					pd.prb = "entry";
> +					n += provide_probe(dtp, &pd);
> +				}
> +				if (prb & FBT_RETURN) {
> +					pd.prb = "return";
> +					n += provide_probe(dtp, &pd);
> +				}
> +
> +			}
> +			sym = dt_symbol_by_name_next(sym);
>   		}
>   
> -#define strstarts(var, x) (strncmp(var, x, strlen (x)) == 0)
> -		/* Weed out __ftrace_invalid_address___* entries. */
> -		if (strstarts(buf, "__ftrace_invalid_address__") ||
> -		    strstarts(buf, "__probestub_") ||
> -		    strstarts(buf, "__traceiter_"))
> +		return n;
> +	}
> +
> +	/*
> +	 * No explicit function name.  We need to go through all possible
> +	 * symbol names and see if they match.
> +	 */
> +	while ((sym = dt_htab_next(dtp->dt_kernsyms, &it)) != NULL) {
> +		dt_module_t	*smp;
> +		const char	*fun;
> +
> +		/* Ensure the symbol can be traced. */
> +		if (!dt_symbol_traceable(sym))
>   			continue;
> -#undef strstarts
>   
> -		/*
> -		 * If we did not see a module name, perform a symbol lookup to
> -		 * try to determine the module name.
> -		 */
> -		if (!p) {
> -			if (dtrace_lookup_by_name(dtp, DTRACE_OBJ_KMODS, buf,
> -						  NULL, &sip) == 0)
> -				mod = sip.object;
> -		} else
> -			mod = p;
> +		/* Match the function name. */
> +		fun = dt_symbol_name(sym);
> +		if (!dt_gmatch(fun, pdp->fun))
> +			continue;
>   
> -		/*
> -		 * Due to the lack of module names in
> -		 * TRACEFS/available_filter_functions, there are some duplicate
> -		 * function names.  The kernel does not let us trace functions
> -		 * that have duplicates, so we need to remove the existing one.
> -		 */
> -		pd.id = DTRACE_IDNONE;
> -		pd.prv = prvname;
> -		pd.mod = mod;
> -		pd.fun = buf;
> -		pd.prb = "entry";
> -		prp = dt_probe_lookup(dtp, &pd);
> -		if (prp != NULL) {
> -			dt_probe_destroy(prp);
> +		/* Validate the module name. */
> +		smp = dt_symbol_module(sym);
> +		if (dmp) {
> +			if (smp != dmp)
> +				continue;
> +		} else if (!dt_gmatch(smp->dm_name, pdp->mod))
>   			continue;
> -		}
>   
> -		if (dt_tp_probe_insert(dtp, prv, prvname, mod, buf, "entry"))
> -			n++;
> -		if (dt_tp_probe_insert(dtp, prv, prvname, mod, buf, "return"))
> -			n++;
> -	}
> +		pd.id = DTRACE_IDNONE;
> +		pd.prv = pdp->prv;
> +		pd.mod = smp->dm_name;
> +		pd.fun = fun;
>   
> -	free(buf);
> -	fclose(f);
> +		if (prb & FBT_ENTRY) {
> +			pd.prb = "entry";
> +			n += provide_probe(dtp, &pd);
> +		}
> +		if (prb & FBT_RETURN) {
> +			pd.prb = "return";
> +			n += provide_probe(dtp, &pd);
> +		}
> +	}
>   
>   	return n;
>   }
> @@ -306,6 +384,7 @@ dt_provimpl_t	dt_rawfbt = {
>   	.name		= prvname,
>   	.prog_type	= BPF_PROG_TYPE_KPROBE,
>   	.populate	= &populate,
> +	.provide	= &provide,
>   	.load_prog	= &dt_bpf_prog_load,
>   	.trampoline	= &trampoline,
>   	.attach		= &attach,