[dpdk-dev] [PATCH] hash: fix to support multi process

De Lara Guarch, Pablo pablo.de.lara.guarch at intel.com
Fri Mar 25 16:08:24 CET 2016


Hi,

> -----Original Message-----
> From: Richardson, Bruce
> Sent: Friday, March 25, 2016 2:41 PM
> To: De Lara Guarch, Pablo
> Cc: dev at dpdk.org; edreddy at gmail.com
> Subject: Re: [PATCH] hash: fix to support multi process
> 
> On Thu, Mar 24, 2016 at 01:56:44PM +0000, Pablo de Lara wrote:
> > Hash library used a function pointer to choose a different
> > key compare function, depending on the key size.
> > As a result, multiple processes could not use the same hash table,
> > as the function addresses vary from one process to another.
> >
> > Instead, a jump table is used, so each process has its own
> > function addresses, accessing this table with an index stored
> > in the hash table (note that using a custom key compare function
> > is not supported in multi-process mode).
> >
> > Fixes: 48a399119619 ("hash: replace with cuckoo hash implementation")
> >
> > Signed-off-by: Pablo de Lara <pablo.de.lara.guarch at intel.com>
> 
> This is a hard problem to solve, but this probably looks the least-worst
> solution
> to it. Pablo, I assume the performance hit for lookups is pretty small here?

Yes, performance degradation is negligible.
> 
> One small nit in the code below, and a comment on the doc change.

Will send a v2 with the changes. Anyway, I was waiting for Djama and Zhang
to give some feedback here and see if it works for them.

Thanks,
Pablo
> Otherwise,
> 
> Acked-by: Bruce Richardson <bruce.richardson at intel.com>
> 
> > ---
> >  doc/guides/rel_notes/release_16_04.rst |  5 ++
> >  lib/librte_hash/rte_cuckoo_hash.c      | 85 ++++++++++++++++++++++++++-
> -------
> >  2 files changed, 71 insertions(+), 19 deletions(-)
> >
> > diff --git a/doc/guides/rel_notes/release_16_04.rst
> b/doc/guides/rel_notes/release_16_04.rst
> > index 2785b29..c4359dd 100644
> > --- a/doc/guides/rel_notes/release_16_04.rst
> > +++ b/doc/guides/rel_notes/release_16_04.rst
> > @@ -351,6 +351,11 @@ Libraries
> >    Fix crc32c hash functions to return a valid crc32c value for data lengths
> >    not multiple of 4 bytes.
> >
> > +* **hash: Fixed hash library to support multi-process mode.**
> > +
> > +  Fix hash library to support multi-process mode, using a jump table,
> > +  instead of storing a function pointer to the key compare function.
> > +
> You probably need to clarify here and in the other docs (e.g. API doc) that:
> * multi-process mode only works with the built-in functions and key sizes.
> * a custom function not in the jump table can be used but only in single-
> process
> mode.
> 
> >  * **librte_port: Fixed segmentation fault for ring and ethdev writer
> nodrop.**
> >
> >    Fixed core dump issue on txq and swq when dropless is set to yes.
> > diff --git a/lib/librte_hash/rte_cuckoo_hash.c
> b/lib/librte_hash/rte_cuckoo_hash.c
> > index 71b5b76..38c19ab 100644
> > --- a/lib/librte_hash/rte_cuckoo_hash.c
> > +++ b/lib/librte_hash/rte_cuckoo_hash.c
> > @@ -102,6 +102,41 @@ EAL_REGISTER_TAILQ(rte_hash_tailq)
> >
> >  #define LCORE_CACHE_SIZE		8
> >
> > +/*
> > + * All different options to select a key compare function,
> > + * based on the key size and custom function.
> > + */
> > +enum cmp_jump_table_case {
> > +	KEY_CUSTOM = 0,
> > +	KEY_16_BYTES,
> > +	KEY_32_BYTES,
> > +	KEY_48_BYTES,
> > +	KEY_64_BYTES,
> > +	KEY_80_BYTES,
> > +	KEY_96_BYTES,
> > +	KEY_112_BYTES,
> > +	KEY_128_BYTES,
> > +	KEY_OTHER_BYTES,
> > +	NUM_KEY_CMP_CASES,
> > +};
> > +
> > +/*
> > + * Table storing all different key compare functions
> > + * (multi-process supported)
> > + */
> > +rte_hash_cmp_eq_t cmp_jump_table[NUM_KEY_CMP_CASES] = {
> > +	NULL,
> > +	rte_hash_k16_cmp_eq,
> > +	rte_hash_k32_cmp_eq,
> > +	rte_hash_k48_cmp_eq,
> > +	rte_hash_k64_cmp_eq,
> > +	rte_hash_k80_cmp_eq,
> > +	rte_hash_k96_cmp_eq,
> > +	rte_hash_k112_cmp_eq,
> > +	rte_hash_k128_cmp_eq,
> > +	memcmp
> > +};
> 
> Array should be const.
> 
> /Bruce



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