Re: [dpdk-dev] [PATCH v2] ring: guarantee ordering of cons/prod loading when doing

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

-----Original Message-----
> Date: Fri, 3 Nov 2017 09:46:40 +0800
> From: Jia He <hejianet@gmail.com>
> To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> Cc: dev@dpdk.org, olivier.matz@6wind.com, konstantin.ananyev@intel.com,
>  bruce.richardson@intel.com, jianbo.liu@arm.com, hemant.agrawal@nxp.com,
>  jie2.liu@hxt-semitech.com, bing.zhao@hxt-semitech.com,
>  jia.he@hxt-semitech.com
> Subject: Re: [PATCH v2] ring: guarantee ordering of cons/prod loading when
>  doing
> User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
>  Thunderbird/52.4.0
> 
> Hi Jerin
> 
> 
> On 11/3/2017 1:23 AM, Jerin Jacob Wrote:
> > -----Original Message-----
> > > Date: Thu,  2 Nov 2017 08:43:30 +0000
> > > From: Jia He <hejianet@gmail.com>
> > > To: jerin.jacob@caviumnetworks.com, dev@dpdk.org, olivier.matz@6wind.com
> > > Cc: konstantin.ananyev@intel.com, bruce.richardson@intel.com,
> > >   jianbo.liu@arm.com, hemant.agrawal@nxp.com, Jia He <hejianet@gmail.com>,
> > >   jie2.liu@hxt-semitech.com, bing.zhao@hxt-semitech.com,
> > >   jia.he@hxt-semitech.com
> > > Subject: [PATCH v2] ring: guarantee ordering of cons/prod loading when doing
> > > X-Mailer: git-send-email 2.7.4
> > > 
> > > We watched a rte panic of mbuf_autotest in our qualcomm arm64 server.
> > > As for the possible race condition, please refer to [1].
> > Hi Jia,
> > 
> > In addition to Konstantin comments. Please find below some review
> > comments.
> > > Furthermore, there are 2 options as suggested by Jerin:
> > > 1. use rte_smp_rmb
> > > 2. use load_acquire/store_release(refer to [2]).
> > > CONFIG_RTE_ATOMIC_ACQUIRE_RELEASE_BARRIER_PREFER is provided, and by
> > I think, The better name would be CONFIG_RTE_RING_USE_C11_MEM_MODEL
> > or something like that.
> Ok, but how to distinguish following 2 options?

No clearly understood this question. For arm64 case, you can add 
CONFIG_RTE_RING_USE_C11_MEM_MODEL=y in config/defconfig_arm64-armv8a-*


> 
> CONFIG_RTE_RING_USE_C11_MEM_MODEL doesn't seem to be enough
> 
> 1. use rte_smp_rmb
> 2. use load_acquire/store_release(refer to [2]).
> 
> > > default it is n;
> > > 
> > > ---
> > > Changelog:
> > > V2: let users choose whether using load_acquire/store_release
> > > V1: rte_smp_rmb() between 2 loads
> > > 
> > > Signed-off-by: Jia He <hejianet@gmail.com>
> > > Signed-off-by: jie2.liu@hxt-semitech.com
> > > Signed-off-by: bing.zhao@hxt-semitech.com
> > > Signed-off-by: jia.he@hxt-semitech.com
> > > Suggested-by: jerin.jacob@caviumnetworks.com
> > > ---
> > >   lib/librte_ring/Makefile           |  4 +++-
> > >   lib/librte_ring/rte_ring.h         | 38 ++++++++++++++++++++++++------
> > >   lib/librte_ring/rte_ring_arm64.h   | 48 ++++++++++++++++++++++++++++++++++++++
> > >   lib/librte_ring/rte_ring_generic.h | 45 +++++++++++++++++++++++++++++++++++
> > >   4 files changed, 127 insertions(+), 8 deletions(-)
> > >   create mode 100644 lib/librte_ring/rte_ring_arm64.h
> > >   create mode 100644 lib/librte_ring/rte_ring_generic.h
> > > 
> > > diff --git a/lib/librte_ring/Makefile b/lib/librte_ring/Makefile
> > > index e34d9d9..fa57a86 100644
> > > --- a/lib/librte_ring/Makefile
> > > +++ b/lib/librte_ring/Makefile
> > > @@ -45,6 +45,8 @@ LIBABIVER := 1
> > >   SRCS-$(CONFIG_RTE_LIBRTE_RING) := rte_ring.c
> > >   # install includes
> > > -SYMLINK-$(CONFIG_RTE_LIBRTE_RING)-include := rte_ring.h
> > > +SYMLINK-$(CONFIG_RTE_LIBRTE_RING)-include := rte_ring.h \
> > > +					rte_ring_arm64.h \
> > It is really not specific to arm64. We could rename it to rte_ring_c11_mem.h or
> > something like that to reflect the implementation based on c11 memory
> > model.
> > 
> > 
> > > +					rte_ring_generic.h
> > >   include $(RTE_SDK)/mk/rte.lib.mk
> > > diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
> > > index 5e9b3b7..943b1f9 100644
> > > --- a/lib/librte_ring/rte_ring.h
> > > +++ b/lib/librte_ring/rte_ring.h
> > > @@ -103,6 +103,18 @@ extern "C" {
> > >   #include <rte_memzone.h>
> > >   #include <rte_pause.h>
> > > +/* In those strong memory models (e.g. x86), there is no need to add rmb()
> > > + * between load and load.
> > > + * In those weak models(powerpc/arm), there are 2 choices for the users
> > > + * 1.use rmb() memory barrier
> > > + * 2.use one-direcion load_acquire/store_release barrier
> > > + * It depends on performance test results. */
> > > +#ifdef RTE_ARCH_ARM64
> > s/RTE_ARCH_ARM64/RTE_RING_USE_C11_MEM_MODEL and update the generic arm64 config.
> > By that way it can used by another architecture like ppc if they choose to do so.
> > 
> > 
> > > +#include "rte_ring_arm64.h"
> > > +#else
> > > +#include "rte_ring_generic.h"
> > > +#endif
> > > +
> > >   #define RTE_TAILQ_RING_NAME "RTE_RING"
> > >   enum rte_ring_queue_behavior {
> > > @@ -368,7 +380,7 @@ update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t new_val,
> > >   		while (unlikely(ht->tail != old_val))
> > >   			rte_pause();
> > > -	ht->tail = new_val;
> > > +	arch_rte_atomic_store(&ht->tail, new_val, __ATOMIC_RELEASE);
> > >   }
> > >   /**
> > > @@ -408,7 +420,8 @@ __rte_ring_move_prod_head(struct rte_ring *r, int is_sp,
> > >   		/* Reset n to the initial burst count */
> > >   		n = max;
> > > -		*old_head = r->prod.head;
> > > +		*old_head = arch_rte_atomic_load(&r->prod.head,
> > > +						__ATOMIC_ACQUIRE);
> > Same as Konstantin comments, i.e move to this function to c11 memory model
> > header file
> > 
> > >   		const uint32_t cons_tail = r->cons.tail;
> > >   		/*
> > >   		 *  The subtraction is done between two unsigned 32bits value
> > > @@ -430,8 +443,10 @@ __rte_ring_move_prod_head(struct rte_ring *r, int is_sp,
> > >   		if (is_sp)
> > >   			r->prod.head = *new_head, success = 1;
> > >   		else
> > > -			success = rte_atomic32_cmpset(&r->prod.head,
> > > -					*old_head, *new_head);
> > > +			success = arch_rte_atomic32_cmpset(&r->prod.head,
> > > +					old_head, *new_head,
> > > +					0, __ATOMIC_ACQUIRE,
> > > +					__ATOMIC_RELAXED);
> > >   	} while (unlikely(success == 0));
> > >   	return n;
> > >   }
> > > @@ -470,7 +485,10 @@ __rte_ring_do_enqueue(struct rte_ring *r, void * const *obj_table,
> > >   		goto end;
> > >   	ENQUEUE_PTRS(r, &r[1], prod_head, obj_table, n, void *);
> > > +
> > > +#ifndef RTE_ATOMIC_ACQUIRE_RELEASE_BARRIER_PREFER
> > This #define will be removed if the function moves.
> > 
> > >   	rte_smp_wmb();
> > > +#endif
> > >   	update_tail(&r->prod, prod_head, prod_next, is_sp);
> > >   end:
> > > @@ -516,7 +534,8 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
> > >   		/* Restore n as it may change every loop */
> > >   		n = max;
> > > -		*old_head = r->cons.head;
> > > +		*old_head = arch_rte_atomic_load(&r->cons.head,
> > > +						__ATOMIC_ACQUIRE);
> > >   		const uint32_t prod_tail = r->prod.tail;
> > >   		/* The subtraction is done between two unsigned 32bits value
> > >   		 * (the result is always modulo 32 bits even if we have
> > > @@ -535,8 +554,10 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
> > >   		if (is_sc)
> > >   			r->cons.head = *new_head, success = 1;
> > >   		else
> > > -			success = rte_atomic32_cmpset(&r->cons.head, *old_head,
> > > -					*new_head);
> > > +			success = arch_rte_atomic32_cmpset(&r->cons.head,
> > > +					old_head, *new_head,
> > > +					0, __ATOMIC_ACQUIRE,
> > > +					__ATOMIC_RELAXED);
> > >   	} while (unlikely(success == 0));
> > >   	return n;
> > >   }
> > > @@ -575,7 +596,10 @@ __rte_ring_do_dequeue(struct rte_ring *r, void **obj_table,
> > >   		goto end;
> > >   	DEQUEUE_PTRS(r, &r[1], cons_head, obj_table, n, void *);
> > > +
> > > +#ifndef RTE_ATOMIC_ACQUIRE_RELEASE_BARRIER_PREFER
> > This #define will be removed if the function moves.
> > 
> > >   	rte_smp_rmb();
> > > +#endif
> 
> -- 
> Cheers,
> Jia
>