Re: [dpdk-dev] [PATCH v2 3/6] lib/lpm: integrate RCU QSBR

["Ruifeng Wang (Arm Technology China)" <Ruifeng.Wang@arm.com>]

Hi Vladimir,

Thanks for your review and  the comments.
All the comments will be addressed in next version.

/Ruifeng

> -----Original Message-----
> From: Medvedkin, Vladimir <vladimir.medvedkin@intel.com>
> Sent: Thursday, September 19, 2019 00:16
> To: Ruifeng Wang (Arm Technology China) <Ruifeng.Wang@arm.com>;
> bruce.richardson@intel.com; olivier.matz@6wind.com
> Cc: dev@dpdk.org; stephen@networkplumber.org;
> konstantin.ananyev@intel.com; Gavin Hu (Arm Technology China)
> <Gavin.Hu@arm.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Dharmik Thakkar
> <Dharmik.Thakkar@arm.com>; nd <nd@arm.com>
> Subject: Re: [PATCH v2 3/6] lib/lpm: integrate RCU QSBR
> 
> Hi Ruifeng,
> 
> Thanks for this patchseries, see comments below.
> 
> On 06/09/2019 10:45, Ruifeng Wang wrote:
> > 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           | 223 +++++++++++++++++++++++++++--
> >   lib/librte_lpm/rte_lpm.h           |  22 +++
> >   lib/librte_lpm/rte_lpm_version.map |   6 +
> >   lib/meson.build                    |   3 +-
> >   6 files changed, 244 insertions(+), 15 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..9764b8de6 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>
> > @@ -22,6 +23,7 @@
> >   #include <rte_rwlock.h>
> >   #include <rte_spinlock.h>
> >   #include <rte_tailq.h>
> > +#include <rte_ring.h>
> >
> >   #include "rte_lpm.h"
> >
> > @@ -39,6 +41,11 @@ enum valid_flag {
> >   	VALID
> >   };
> >
> > +struct __rte_lpm_qs_item {
> > +	uint64_t token;	/**< QSBR token.*/
> > +	uint32_t index;	/**< tbl8 group index.*/
> > +};
> > +
> >   /* Macro to enable/disable run-time checks. */
> >   #if defined(RTE_LIBRTE_LPM_DEBUG)
> >   #include <rte_debug.h>
> > @@ -381,6 +388,7 @@ rte_lpm_free_v1604(struct rte_lpm *lpm)
> >
> >   	rte_mcfg_tailq_write_unlock();
> >
> > +	rte_ring_free(lpm->qs_fifo);
> >   	rte_free(lpm->tbl8);
> >   	rte_free(lpm->rules_tbl);
> >   	rte_free(lpm);
> > @@ -390,6 +398,147 @@ BIND_DEFAULT_SYMBOL(rte_lpm_free, _v1604,
> 16.04);
> >   MAP_STATIC_SYMBOL(void rte_lpm_free(struct rte_lpm *lpm),
> >   		rte_lpm_free_v1604);
> >
> > +/* Add an item into FIFO.
> > + * return: 0 - success
> > + */
> > +static int
> > +__rte_lpm_rcu_qsbr_fifo_push(struct rte_ring *fifo,
> > +	struct __rte_lpm_qs_item *item)
> > +{
> > +	if (rte_ring_free_count(fifo) < 2) {
> > +		RTE_LOG(ERR, LPM, "QS FIFO full\n");
> > +		rte_errno = ENOSPC;
> > +		return 1;
> > +	}
> > +
> > +	(void)rte_ring_sp_enqueue(fifo, (void *)(uintptr_t)item->token);
> > +	(void)rte_ring_sp_enqueue(fifo, (void *)(uintptr_t)item->index);
> > +
> > +	return 0;
> > +}
> > +
> > +/* Remove item from FIFO.
> > + * Used when data observed by rte_ring_peek.
> > + */
> > +static void
> > +__rte_lpm_rcu_qsbr_fifo_pop(struct rte_ring *fifo,
> > +	struct __rte_lpm_qs_item *item)
> Is it necessary to pass the pointer for struct __rte_lpm_qs_item?
> According to code only item.index is used after this call.
> > +{
> > +	void *obj_token = NULL;
> > +	void *obj_index = NULL;
> > +
> > +	(void)rte_ring_sc_dequeue(fifo, &obj_token);
> I think it is not necessary to cast here.
> > +	(void)rte_ring_sc_dequeue(fifo, &obj_index);
> > +
> > +	if (item) {
> I think it is redundant, it is always not NULL.
> > +		item->token = (uint64_t)((uintptr_t)obj_token);
> > +		item->index = (uint32_t)((uintptr_t)obj_index);
> > +	}
> > +}
> > +
> > +/* Max number of tbl8 groups to reclaim at one time. */
> > +#define RCU_QSBR_RECLAIM_SIZE	8
> > +
> > +/* When RCU QSBR FIFO usage is above
> 1/(2^RCU_QSBR_RECLAIM_LEVEL),
> > + * reclaim will be triggered by tbl8_free.
> > + */
> > +#define RCU_QSBR_RECLAIM_LEVEL	3
> > +
> > +/* Reclaim some tbl8 groups based on quiescent state check.
> > + * RCU_QSBR_RECLAIM_SIZE groups will be reclaimed at max.
> > + * Params: lpm   - lpm object handle
> > + *         index - (onput) one of successfully reclaimed tbl8 groups
> > + * return: 0 - success, 1 - no group reclaimed.
> > + */
> > +static uint32_t
> > +__rte_lpm_rcu_qsbr_reclaim_chunk(struct rte_lpm *lpm, uint32_t
> > +*index) {
> > +	struct __rte_lpm_qs_item qs_item;
> > +	struct rte_lpm_tbl_entry *tbl8_entry = NULL;
> It is not necessary to init it with NULL.
> > +	void *obj_token;
> > +	uint32_t cnt = 0;
> > +
> > +	RTE_LOG(DEBUG, LPM, "RCU QSBR reclaimation triggered.\n");
> > +	/* Check reader threads quiescent state and
> > +	 * reclaim as much tbl8 groups as possible.
> > +	 */
> > +	while ((cnt < RCU_QSBR_RECLAIM_SIZE) &&
> > +		(rte_ring_peek(lpm->qs_fifo, &obj_token) == 0) &&
> > +		(rte_rcu_qsbr_check(lpm->qsv,
> (uint64_t)((uintptr_t)obj_token),
> > +					false) == 1)) {
> > +		__rte_lpm_rcu_qsbr_fifo_pop(lpm->qs_fifo, &qs_item);
> > +
> > +		tbl8_entry = &lpm->tbl8[qs_item.index *
> > +
> 	RTE_LPM_TBL8_GROUP_NUM_ENTRIES];
> > +		memset(&tbl8_entry[0], 0,
> > +				RTE_LPM_TBL8_GROUP_NUM_ENTRIES *
> > +				sizeof(tbl8_entry[0]));
> > +		cnt++;
> > +	}
> > +
> > +	RTE_LOG(DEBUG, LPM, "RCU QSBR reclaimed %u groups.\n", cnt);
> > +	if (cnt) {
> > +		if (index)
> > +			*index = qs_item.index;
> > +		return 0;
> > +	}
> > +	return 1;
> > +}
> > +
> > +/* Trigger tbl8 group reclaim when necessary.
> > + * Reclaim happens when RCU QSBR queue usage
> > + * is over 1/(2^RCU_QSBR_RECLAIM_LEVEL).
> > + */
> > +static void
> > +__rte_lpm_rcu_qsbr_try_reclaim(struct rte_lpm *lpm) {
> > +	if (lpm->qsv == NULL)
> > +		return;
> This check is redundant.
> > +
> > +	if (rte_ring_count(lpm->qs_fifo) <
> > +		(rte_ring_get_capacity(lpm->qs_fifo) >>
> RCU_QSBR_RECLAIM_LEVEL))
> > +		return;
> > +
> > +	(void)__rte_lpm_rcu_qsbr_reclaim_chunk(lpm, NULL); }
> > +
> > +/* Associate QSBR variable with an LPM object.
> > + */
> > +int
> > +rte_lpm_rcu_qsbr_add(struct rte_lpm *lpm, struct rte_rcu_qsbr *v) {
> > +	uint32_t qs_fifo_size;
> > +	char rcu_ring_name[RTE_RING_NAMESIZE];
> > +
> > +	if ((lpm == NULL) || (v == NULL)) {
> > +		rte_errno = EINVAL;
> > +		return 1;
> > +	}
> > +
> > +	if (lpm->qsv) {
> > +		rte_errno = EEXIST;
> > +		return 1;
> > +	}
> > +
> > +	/* round up qs_fifo_size to next power of two that is not less than
> > +	 * number_tbl8s. Will store 'token' and 'index'.
> > +	 */
> > +	qs_fifo_size = rte_align32pow2((2 * lpm->number_tbl8s) + 1);
> > +
> > +	/* Init QSBR reclaiming FIFO. */
> > +	snprintf(rcu_ring_name, sizeof(rcu_ring_name), "LPM_RCU_%s",
> lpm->name);
> > +	lpm->qs_fifo = rte_ring_create(rcu_ring_name, qs_fifo_size,
> > +					SOCKET_ID_ANY, 0);
> > +	if (lpm->qs_fifo == NULL) {
> > +		RTE_LOG(ERR, LPM, "LPM QS FIFO memory allocation
> failed\n");
> > +		rte_errno = ENOMEM;
> rte_ring_create() sets rte_errno on error, I don't think we need to rewrite it
> here.
> > +		return 1;
> > +	}
> > +	lpm->qsv = v;
> > +
> > +	return 0;
> > +}
> > +
> >   /*
> >    * Adds a rule to the rule table.
> >    *
> > @@ -640,6 +789,35 @@ rule_find_v1604(struct rte_lpm *lpm, uint32_t
> ip_masked, uint8_t depth)
> >   	return -EINVAL;
> >   }
> >
> > +static int32_t
> > +tbl8_alloc_reclaimed(struct rte_lpm *lpm) {
> > +	struct rte_lpm_tbl_entry *tbl8_entry = NULL;
> > +	uint32_t index;
> > +
> > +	if (lpm->qsv != NULL) {
> > +		if (__rte_lpm_rcu_qsbr_reclaim_chunk(lpm, &index) == 0) {
> > +			/* Set the last reclaimed tbl8 group as VALID. */
> > +			struct rte_lpm_tbl_entry new_tbl8_entry = {
> > +				.next_hop = 0,
> > +				.valid = INVALID,
> > +				.depth = 0,
> > +				.valid_group = VALID,
> > +			};
> > +
> > +			tbl8_entry = &lpm->tbl8[index *
> > +
> 	RTE_LPM_TBL8_GROUP_NUM_ENTRIES];
> > +			__atomic_store(tbl8_entry, &new_tbl8_entry,
> > +					__ATOMIC_RELAXED);
> > +
> > +			/* Return group index for reclaimed tbl8 group. */
> > +			return index;
> > +		}
> > +	}
> > +
> > +	return -ENOSPC;
> > +}
> > +
> >   /*
> >    * Find, clean and allocate a tbl8.
> >    */
> > @@ -679,14 +857,15 @@ 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 = { @@ -
> 708,8 +887,8 @@
> > tbl8_alloc_v1604(struct rte_lpm_tbl_entry *tbl8, uint32_t number_tbl8s)
> >   		}
> >   	}
> >
> > -	/* If there are no tbl8 groups free then return error. */
> > -	return -ENOSPC;
> > +	/* If there are no tbl8 groups free then check reclaim queue. */
> > +	return tbl8_alloc_reclaimed(lpm);
> >   }
> >
> >   static void
> > @@ -728,13 +907,31 @@ 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_qs_item qs_item;
> >   	struct rte_lpm_tbl_entry zero_tbl8_entry = {0};
> >
> > -	__atomic_store(&tbl8[tbl8_group_start], &zero_tbl8_entry,
> > -			__ATOMIC_RELAXED);
> > +	if (lpm->qsv != NULL) {
> > +		/* Push into QSBR FIFO. */
> > +		qs_item.token = rte_rcu_qsbr_start(lpm->qsv);
> > +		qs_item.index =
> > +			tbl8_group_start /
> RTE_LPM_TBL8_GROUP_NUM_ENTRIES;
> > +		if (__rte_lpm_rcu_qsbr_fifo_push(lpm->qs_fifo,
> &qs_item) != 0)
> > +			/* This should never happen as FIFO size is big
> enough
> > +			 * to hold all tbl8 groups.
> > +			 */
> > +			RTE_LOG(ERR, LPM, "Failed to push QSBR FIFO\n");
> > +
> > +		/* Speculatively reclaim tbl8 groups.
> > +		 * Help spread the reclaim work load across multiple calls.
> > +		 */
> > +		__rte_lpm_rcu_qsbr_try_reclaim(lpm);
> > +	} else {
> > +		/* Set tbl8 group invalid*/
> > +		__atomic_store(&lpm->tbl8[tbl8_group_start],
> &zero_tbl8_entry,
> > +				__ATOMIC_RELAXED);
> > +	}
> >   }
> >
> >   static __rte_noinline int32_t
> > @@ -1037,7 +1234,7 @@ 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 +1280,7 @@ 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 +2015,7 @@ 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
> +2031,7 @@
> > 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..5079fb262 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 +188,8 @@ 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 *qsv;	/**< RCU QSBR variable for tbl8
> group.*/
> > +	struct rte_ring *qs_fifo;	/**< RCU QSBR reclaiming queue. */
> >   };
> >
> >   /**
> > @@ -248,6 +252,24 @@ 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;
> > +};
> > diff --git a/lib/meson.build b/lib/meson.build index
> > e5ff83893..3a96f005d 100644
> > --- a/lib/meson.build
> > +++ b/lib/meson.build
> > @@ -11,6 +11,7 @@
> >   libraries = [
> >   	'kvargs', # eal depends on kvargs
> >   	'eal', # everything depends on eal
> > +	'rcu', # hash and lpm depends on this
> >   	'ring', 'mempool', 'mbuf', 'net', 'meter', 'ethdev', 'pci', # core
> >   	'cmdline',
> >   	'metrics', # bitrate/latency stats depends on this @@ -22,7 +23,7
> > @@ libraries = [
> >   	'gro', 'gso', 'ip_frag', 'jobstats',
> >   	'kni', 'latencystats', 'lpm', 'member',
> >   	'power', 'pdump', 'rawdev',
> > -	'rcu', 'reorder', 'sched', 'security', 'stack', 'vhost',
> > +	'reorder', 'sched', 'security', 'stack', 'vhost',
> >   	# ipsec lib depends on net, crypto and security
> >   	'ipsec',
> >   	# add pkt framework libs which use other libs from above
> 
> --
> Regards,
> Vladimir