Re: [dpdk-dev] [PATCH v3 1/3] lib/lpm: integrate RCU QSBR

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> 
> Hi Honnappa,
> 
> On 01/10/2019 19:28, Honnappa Nagarahalli wrote:
> > From: Ruifeng Wang <ruifeng.wang@arm.com>
> >
> > Currently, the tbl8 group is freed even though the readers might be
> > using the tbl8 group entries. The freed tbl8 group can be reallocated
> > quickly. This results in incorrect lookup results.
> >
> > RCU QSBR process is integrated for safe tbl8 group reclaim.
> > Refer to RCU documentation to understand various aspects of
> > integrating RCU library into other libraries.
> >
> > Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > ---
> >   lib/librte_lpm/Makefile            |   3 +-
> >   lib/librte_lpm/meson.build         |   2 +
> >   lib/librte_lpm/rte_lpm.c           | 102 +++++++++++++++++++++++++----
> >   lib/librte_lpm/rte_lpm.h           |  21 ++++++
> >   lib/librte_lpm/rte_lpm_version.map |   6 ++
> >   5 files changed, 122 insertions(+), 12 deletions(-)
> >
> > diff --git a/lib/librte_lpm/Makefile b/lib/librte_lpm/Makefile index
> > a7946a1c5..ca9e16312 100644
> > --- a/lib/librte_lpm/Makefile
> > +++ b/lib/librte_lpm/Makefile
> > @@ -6,9 +6,10 @@ include $(RTE_SDK)/mk/rte.vars.mk
> >   # library name
> >   LIB = librte_lpm.a
> >
> > +CFLAGS += -DALLOW_EXPERIMENTAL_API
> >   CFLAGS += -O3
> >   CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -LDLIBS += -lrte_eal
> > -lrte_hash
> > +LDLIBS += -lrte_eal -lrte_hash -lrte_rcu
> >
> >   EXPORT_MAP := rte_lpm_version.map
> >
> > diff --git a/lib/librte_lpm/meson.build b/lib/librte_lpm/meson.build
> > index a5176d8ae..19a35107f 100644
> > --- a/lib/librte_lpm/meson.build
> > +++ b/lib/librte_lpm/meson.build
> > @@ -2,9 +2,11 @@
> >   # Copyright(c) 2017 Intel Corporation
> >
> >   version = 2
> > +allow_experimental_apis = true
> >   sources = files('rte_lpm.c', 'rte_lpm6.c')
> >   headers = files('rte_lpm.h', 'rte_lpm6.h')
> >   # since header files have different names, we can install all vector headers
> >   # without worrying about which architecture we actually need
> >   headers += files('rte_lpm_altivec.h', 'rte_lpm_neon.h', 'rte_lpm_sse.h')
> >   deps += ['hash']
> > +deps += ['rcu']
> > diff --git a/lib/librte_lpm/rte_lpm.c b/lib/librte_lpm/rte_lpm.c index
> > 3a929a1b1..ca58d4b35 100644
> > --- a/lib/librte_lpm/rte_lpm.c
> > +++ b/lib/librte_lpm/rte_lpm.c
> > @@ -1,5 +1,6 @@
> >   /* SPDX-License-Identifier: BSD-3-Clause
> >    * Copyright(c) 2010-2014 Intel Corporation
> > + * Copyright(c) 2019 Arm Limited
> >    */
> >
> >   #include <string.h>
> > @@ -381,6 +382,8 @@ rte_lpm_free_v1604(struct rte_lpm *lpm)
> >
> >   	rte_mcfg_tailq_write_unlock();
> >
> > +	if (lpm->dq)
> > +		rte_rcu_qsbr_dq_delete(lpm->dq);
> >   	rte_free(lpm->tbl8);
> >   	rte_free(lpm->rules_tbl);
> >   	rte_free(lpm);
> > @@ -390,6 +393,59 @@ BIND_DEFAULT_SYMBOL(rte_lpm_free, _v1604,
> 16.04);
> >   MAP_STATIC_SYMBOL(void rte_lpm_free(struct rte_lpm *lpm),
> >   		rte_lpm_free_v1604);
> As a general comment, are you going to add rcu support to the legacy _v20 ?
I do not see a requirement from my side. What's your suggestion?

> >
> > +struct __rte_lpm_rcu_dq_entry {
> > +	uint32_t tbl8_group_index;
> > +	uint32_t pad;
> > +};
> 
> Is this struct necessary? I mean in tbl8_free_v1604() you can pass
> tbl8_group_index as a pointer without "e.pad = 0;".
Agree, that is another way. This structure will go away once the ring library supports storing 32b elements.

> 
> And what about 32bit environment?
Waiting for rte_ring to support 32b elements (the patch is being discussed).

> 
> > +
> > +static void
> > +__lpm_rcu_qsbr_free_resource(void *p, void *data) {
> > +	struct rte_lpm_tbl_entry zero_tbl8_entry = {0};
> > +	struct __rte_lpm_rcu_dq_entry *e =
> > +			(struct __rte_lpm_rcu_dq_entry *)data;
> > +	struct rte_lpm_tbl_entry *tbl8 = (struct rte_lpm_tbl_entry *)p;
> > +
> > +	/* Set tbl8 group invalid */
> > +	__atomic_store(&tbl8[e->tbl8_group_index], &zero_tbl8_entry,
> > +		__ATOMIC_RELAXED);
> > +}
> > +
> > +/* Associate QSBR variable with an LPM object.
> > + */
> > +int
> > +rte_lpm_rcu_qsbr_add(struct rte_lpm *lpm, struct rte_rcu_qsbr *v) {
> > +	char rcu_dq_name[RTE_RCU_QSBR_DQ_NAMESIZE];
> > +	struct rte_rcu_qsbr_dq_parameters params;
> > +
> > +	if ((lpm == NULL) || (v == NULL)) {
> > +		rte_errno = EINVAL;
> > +		return 1;
> > +	}
> > +
> > +	if (lpm->dq) {
> > +		rte_errno = EEXIST;
> > +		return 1;
> > +	}
> > +
> > +	/* Init QSBR defer queue. */
> > +	snprintf(rcu_dq_name, sizeof(rcu_dq_name), "LPM_RCU_%s", lpm-
> >name);
> 
> Consider moving this logic into rte_rcu_qsbr_dq_create(). I think there you
> could prefix the name with just RCU_ . So it would be possible to move
> include <rte_ring.h> into the rte_rcu_qsbr.c from rte_rcu_qsbr.h and get rid
> of RTE_RCU_QSBR_DQ_NAMESIZE macro in rte_rcu_qsbr.h file.
Macro is required to provide a length for the name, similar to what rte_ring does. What would be the length of the 'name' if RTE_RCU_QSBR_DQ_NAMESIZE is removed?
If the 'RCU_' has to be prefixed in 'rte_rcu_qsbr_dq_create', then RTE_RCU_QSBR_DQ_NAMESIZE needs to be readjusted in the header file. I am trying to keep it simple by constructing the string in a single function.

> 
> > +	params.name = rcu_dq_name;
> > +	params.size = lpm->number_tbl8s;
> > +	params.esize = sizeof(struct __rte_lpm_rcu_dq_entry);
> > +	params.f = __lpm_rcu_qsbr_free_resource;
> > +	params.p = lpm->tbl8;
> > +	params.v = v;
> > +	lpm->dq = rte_rcu_qsbr_dq_create(&params);
> > +	if (lpm->dq == NULL) {
> > +		RTE_LOG(ERR, LPM, "LPM QS defer queue creation failed\n");
> > +		return 1;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >   /*
> >    * Adds a rule to the rule table.
> >    *
> > @@ -679,14 +735,15 @@ tbl8_alloc_v20(struct rte_lpm_tbl_entry_v20
> *tbl8)
> >   }
> >
> >   static int32_t
> > -tbl8_alloc_v1604(struct rte_lpm_tbl_entry *tbl8, uint32_t
> > number_tbl8s)
> > +__tbl8_alloc_v1604(struct rte_lpm *lpm)
> >   {
> >   	uint32_t group_idx; /* tbl8 group index. */
> >   	struct rte_lpm_tbl_entry *tbl8_entry;
> >
> >   	/* Scan through tbl8 to find a free (i.e. INVALID) tbl8 group. */
> > -	for (group_idx = 0; group_idx < number_tbl8s; group_idx++) {
> > -		tbl8_entry = &tbl8[group_idx *
> RTE_LPM_TBL8_GROUP_NUM_ENTRIES];
> > +	for (group_idx = 0; group_idx < lpm->number_tbl8s; group_idx++) {
> > +		tbl8_entry = &lpm->tbl8[group_idx *
> > +
> 	RTE_LPM_TBL8_GROUP_NUM_ENTRIES];
> >   		/* If a free tbl8 group is found clean it and set as VALID. */
> >   		if (!tbl8_entry->valid_group) {
> >   			struct rte_lpm_tbl_entry new_tbl8_entry = { @@ -
> 712,6 +769,21 @@
> > tbl8_alloc_v1604(struct rte_lpm_tbl_entry *tbl8, uint32_t number_tbl8s)
> >   	return -ENOSPC;
> >   }
> >
> > +static int32_t
> > +tbl8_alloc_v1604(struct rte_lpm *lpm) {
> > +	int32_t group_idx; /* tbl8 group index. */
> > +
> > +	group_idx = __tbl8_alloc_v1604(lpm);
> > +	if ((group_idx < 0) && (lpm->dq != NULL)) {
> > +		/* If there are no tbl8 groups try to reclaim some. */
> > +		if (rte_rcu_qsbr_dq_reclaim(lpm->dq) == 0)
> > +			group_idx = __tbl8_alloc_v1604(lpm);
> > +	}
> > +
> > +	return group_idx;
> > +}
> > +
> >   static void
> >   tbl8_free_v20(struct rte_lpm_tbl_entry_v20 *tbl8, uint32_t
> tbl8_group_start)
> >   {
> > @@ -728,13 +800,21 @@ tbl8_free_v20(struct rte_lpm_tbl_entry_v20
> *tbl8, uint32_t tbl8_group_start)
> >   }
> >
> >   static void
> > -tbl8_free_v1604(struct rte_lpm_tbl_entry *tbl8, uint32_t
> > tbl8_group_start)
> > +tbl8_free_v1604(struct rte_lpm *lpm, uint32_t tbl8_group_start)
> >   {
> > -	/* Set tbl8 group invalid*/
> >   	struct rte_lpm_tbl_entry zero_tbl8_entry = {0};
> > +	struct __rte_lpm_rcu_dq_entry e;
> >
> > -	__atomic_store(&tbl8[tbl8_group_start], &zero_tbl8_entry,
> > -			__ATOMIC_RELAXED);
> > +	if (lpm->dq != NULL) {
> > +		e.tbl8_group_index = tbl8_group_start;
> > +		e.pad = 0;
> > +		/* Push into QSBR defer queue. */
> > +		rte_rcu_qsbr_dq_enqueue(lpm->dq, (void *)&e);
> > +	} else {
> > +		/* Set tbl8 group invalid*/
> > +		__atomic_store(&lpm->tbl8[tbl8_group_start],
> &zero_tbl8_entry,
> > +				__ATOMIC_RELAXED);
> > +	}
> >   }
> >
> >   static __rte_noinline int32_t
> > @@ -1037,7 +1117,7 @@ add_depth_big_v1604(struct rte_lpm *lpm,
> > uint32_t ip_masked, uint8_t depth,
> >
> >   	if (!lpm->tbl24[tbl24_index].valid) {
> >   		/* Search for a free tbl8 group. */
> > -		tbl8_group_index = tbl8_alloc_v1604(lpm->tbl8, lpm-
> >number_tbl8s);
> > +		tbl8_group_index = tbl8_alloc_v1604(lpm);
> >
> >   		/* Check tbl8 allocation was successful. */
> >   		if (tbl8_group_index < 0) {
> > @@ -1083,7 +1163,7 @@ add_depth_big_v1604(struct rte_lpm *lpm,
> uint32_t ip_masked, uint8_t depth,
> >   	} /* If valid entry but not extended calculate the index into Table8. */
> >   	else if (lpm->tbl24[tbl24_index].valid_group == 0) {
> >   		/* Search for free tbl8 group. */
> > -		tbl8_group_index = tbl8_alloc_v1604(lpm->tbl8, lpm-
> >number_tbl8s);
> > +		tbl8_group_index = tbl8_alloc_v1604(lpm);
> >
> >   		if (tbl8_group_index < 0) {
> >   			return tbl8_group_index;
> > @@ -1818,7 +1898,7 @@ delete_depth_big_v1604(struct rte_lpm *lpm,
> uint32_t ip_masked,
> >   		 */
> >   		lpm->tbl24[tbl24_index].valid = 0;
> >   		__atomic_thread_fence(__ATOMIC_RELEASE);
> > -		tbl8_free_v1604(lpm->tbl8, tbl8_group_start);
> > +		tbl8_free_v1604(lpm, tbl8_group_start);
> >   	} else if (tbl8_recycle_index > -1) {
> >   		/* Update tbl24 entry. */
> >   		struct rte_lpm_tbl_entry new_tbl24_entry = { @@ -1834,7
> +1914,7 @@
> > delete_depth_big_v1604(struct rte_lpm *lpm, uint32_t ip_masked,
> >   		__atomic_store(&lpm->tbl24[tbl24_index],
> &new_tbl24_entry,
> >   				__ATOMIC_RELAXED);
> >   		__atomic_thread_fence(__ATOMIC_RELEASE);
> > -		tbl8_free_v1604(lpm->tbl8, tbl8_group_start);
> > +		tbl8_free_v1604(lpm, tbl8_group_start);
> >   	}
> >   #undef group_idx
> >   	return 0;
> > diff --git a/lib/librte_lpm/rte_lpm.h b/lib/librte_lpm/rte_lpm.h index
> > 906ec4483..49c12a68d 100644
> > --- a/lib/librte_lpm/rte_lpm.h
> > +++ b/lib/librte_lpm/rte_lpm.h
> > @@ -1,5 +1,6 @@
> >   /* SPDX-License-Identifier: BSD-3-Clause
> >    * Copyright(c) 2010-2014 Intel Corporation
> > + * Copyright(c) 2019 Arm Limited
> >    */
> >
> >   #ifndef _RTE_LPM_H_
> > @@ -21,6 +22,7 @@
> >   #include <rte_common.h>
> >   #include <rte_vect.h>
> >   #include <rte_compat.h>
> > +#include <rte_rcu_qsbr.h>
> >
> >   #ifdef __cplusplus
> >   extern "C" {
> > @@ -186,6 +188,7 @@ struct rte_lpm {
> >   			__rte_cache_aligned; /**< LPM tbl24 table. */
> >   	struct rte_lpm_tbl_entry *tbl8; /**< LPM tbl8 table. */
> >   	struct rte_lpm_rule *rules_tbl; /**< LPM rules. */
> > +	struct rte_rcu_qsbr_dq *dq;	/**< RCU QSBR defer queue.*/
> >   };
> >
> >   /**
> > @@ -248,6 +251,24 @@ rte_lpm_free_v20(struct rte_lpm_v20 *lpm);
> >   void
> >   rte_lpm_free_v1604(struct rte_lpm *lpm);
> >
> > +/**
> > + * Associate RCU QSBR variable with an LPM object.
> > + *
> > + * @param lpm
> > + *   the lpm object to add RCU QSBR
> > + * @param v
> > + *   RCU QSBR variable
> > + * @return
> > + *   On success - 0
> > + *   On error - 1 with error code set in rte_errno.
> > + *   Possible rte_errno codes are:
> > + *   - EINVAL - invalid pointer
> > + *   - EEXIST - already added QSBR
> > + *   - ENOMEM - memory allocation failure
> > + */
> > +__rte_experimental
> > +int rte_lpm_rcu_qsbr_add(struct rte_lpm *lpm, struct rte_rcu_qsbr
> > +*v);
> > +
> >   /**
> >    * Add a rule to the LPM table.
> >    *
> > diff --git a/lib/librte_lpm/rte_lpm_version.map
> > b/lib/librte_lpm/rte_lpm_version.map
> > index 90beac853..b353aabd2 100644
> > --- a/lib/librte_lpm/rte_lpm_version.map
> > +++ b/lib/librte_lpm/rte_lpm_version.map
> > @@ -44,3 +44,9 @@ DPDK_17.05 {
> >   	rte_lpm6_lookup_bulk_func;
> >
> >   } DPDK_16.04;
> > +
> > +EXPERIMENTAL {
> > +	global:
> > +
> > +	rte_lpm_rcu_qsbr_add;
> > +};
> 
> --
> Regards,
> Vladimir