[dpdk-dev] [PATCH v4 3/3] lib/lpm: use atomic store to avoid partial update
Honnappa Nagarahalli
Honnappa.Nagarahalli at arm.com
Tue Jul 9 06:43:19 CEST 2019
> >
> > >
> > > Compiler could generate non-atomic stores for whole table entry updating.
> > > This may cause incorrect nexthop to be returned, if the byte with
> > > valid flag is updated prior to the byte with next hot is updated.
> > ^^^^^^^
> > Should be nexthop
> >
> > >
> > > Changed to use atomic store to update whole table entry.
> > >
> > > Suggested-by: Medvedkin Vladimir <vladimir.medvedkin at intel.com>
> > > Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
> > > Reviewed-by: Gavin Hu <gavin.hu at arm.com>
> > > ---
> > > v4: initial version
> > >
> > > lib/librte_lpm/rte_lpm.c | 34 ++++++++++++++++++++++++----------
> > > 1 file changed, 24 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/lib/librte_lpm/rte_lpm.c b/lib/librte_lpm/rte_lpm.c
> > > index
> > > baa6e7460..5d1dbd7e6 100644
> > > --- a/lib/librte_lpm/rte_lpm.c
> > > +++ b/lib/librte_lpm/rte_lpm.c
> > > @@ -767,7 +767,9 @@ add_depth_small_v20(struct rte_lpm_v20 *lpm,
> > > uint32_t ip, uint8_t depth,
> > > * Setting tbl8 entry in one go to avoid
> > > * race conditions
> > > */
> > > - lpm->tbl8[j] = new_tbl8_entry;
> > > + __atomic_store(&lpm->tbl8[j],
> > > + &new_tbl8_entry,
> > > + __ATOMIC_RELAXED);
> > >
> > > continue;
> > > }
> > > @@ -837,7 +839,9 @@ add_depth_small_v1604(struct rte_lpm *lpm,
> > > uint32_t ip, uint8_t depth,
> > > * Setting tbl8 entry in one go to avoid
> > > * race conditions
> > > */
> > > - lpm->tbl8[j] = new_tbl8_entry;
> > > + __atomic_store(&lpm->tbl8[j],
> > > + &new_tbl8_entry,
> > > + __ATOMIC_RELAXED);
> > >
> > > continue;
> > > }
> > > @@ -965,7 +969,8 @@ add_depth_big_v20(struct rte_lpm_v20 *lpm,
> > > uint32_t ip_masked, uint8_t depth,
> > > * Setting tbl8 entry in one go to avoid race
> > > * condition
> > > */
> > > - lpm->tbl8[i] = new_tbl8_entry;
> > > + __atomic_store(&lpm->tbl8[i],
> > > &new_tbl8_entry,
> > > + __ATOMIC_RELAXED);
> > >
> > > continue;
> > > }
> > > @@ -1100,7 +1105,8 @@ add_depth_big_v1604(struct rte_lpm *lpm,
> > > uint32_t ip_masked, uint8_t depth,
> > > * Setting tbl8 entry in one go to avoid race
> > > * condition
> > > */
> > > - lpm->tbl8[i] = new_tbl8_entry;
> > > + __atomic_store(&lpm->tbl8[i],
> > > &new_tbl8_entry,
> > > + __ATOMIC_RELAXED);
> > >
> > > continue;
> > > }
> > > @@ -1393,7 +1399,9 @@ delete_depth_small_v20(struct rte_lpm_v20
> > *lpm,
> > > uint32_t ip_masked,
> > >
> > > RTE_LPM_TBL8_GROUP_NUM_ENTRIES); j++) {
> > >
> > > if (lpm->tbl8[j].depth <= depth)
> > > - lpm->tbl8[j] =
> > > new_tbl8_entry;
> > > + __atomic_store(&lpm-
> > >tbl8[j],
> > > + &new_tbl8_entry,
> > > + __ATOMIC_RELAXED);
> > > }
> > > }
> > > }
> > > @@ -1490,7 +1498,9 @@ delete_depth_small_v1604(struct rte_lpm *lpm,
> > > uint32_t ip_masked,
> > >
> > > RTE_LPM_TBL8_GROUP_NUM_ENTRIES); j++) {
> > >
> > > if (lpm->tbl8[j].depth <= depth)
> > > - lpm->tbl8[j] =
> > > new_tbl8_entry;
> > > + __atomic_store(&lpm-
> > >tbl8[j],
> > > + &new_tbl8_entry,
> > > + __ATOMIC_RELAXED);
> > > }
> > > }
> > > }
> > > @@ -1646,7 +1656,8 @@ delete_depth_big_v20(struct rte_lpm_v20 *lpm,
> > > uint32_t ip_masked,
> > > */
> > > for (i = tbl8_index; i < (tbl8_index + tbl8_range); i++) {
> > > if (lpm->tbl8[i].depth <= depth)
> > > - lpm->tbl8[i] = new_tbl8_entry;
> > > + __atomic_store(&lpm->tbl8[i],
> > > &new_tbl8_entry,
> > > + __ATOMIC_RELAXED);
> > > }
> > > }
> > >
> > > @@ -1677,7 +1688,8 @@ delete_depth_big_v20(struct rte_lpm_v20 *lpm,
> > > uint32_t ip_masked,
> > > /* Set tbl24 before freeing tbl8 to avoid race condition.
> > > * Prevent the free of the tbl8 group from hoisting.
> > > */
> > > - lpm->tbl24[tbl24_index] = new_tbl24_entry;
> > > + __atomic_store(&lpm->tbl24[tbl24_index],
> > > &new_tbl24_entry,
> > > + __ATOMIC_RELAXED);
> > > __atomic_thread_fence(__ATOMIC_RELEASE);
> > > tbl8_free_v20(lpm->tbl8, tbl8_group_start);
> > tbl8_alloc_v20/tbl8_free_v20 need to be updated to use __atomic_store
> >
> tbl8_alloc_v20/tbl8_free_v20 updates a single field of table entry. The process
> is already atomic. Do we really need to use __atomic_store?
I thought we agreed that all the tbl8 stores will use __atomic_store.
IMO, it is better to use C11 atomic built-ins entirely, at least for the data structures used in reader-writer scenario. Otherwise, the code does not follow C11 memory model completely. (I do not know what to call such a model).
>
> > > }
> > > @@ -1730,7 +1742,8 @@ delete_depth_big_v1604(struct rte_lpm *lpm,
> > > uint32_t ip_masked,
> > > */
> > > for (i = tbl8_index; i < (tbl8_index + tbl8_range); i++) {
> > > if (lpm->tbl8[i].depth <= depth)
> > > - lpm->tbl8[i] = new_tbl8_entry;
> > > + __atomic_store(&lpm->tbl8[i],
> > > &new_tbl8_entry,
> > > + __ATOMIC_RELAXED);
> > > }
> > > }
> > >
> > > @@ -1761,7 +1774,8 @@ delete_depth_big_v1604(struct rte_lpm *lpm,
> > > uint32_t ip_masked,
> > > /* Set tbl24 before freeing tbl8 to avoid race condition.
> > > * Prevent the free of the tbl8 group from hoisting.
> > > */
> > > - lpm->tbl24[tbl24_index] = new_tbl24_entry;
> > > + __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_alloc_v1604 /tbl8_free_v1604 need to be updated to use
> > __atomic_store
> Ditto.
>
> >
> > > }
> > > --
> > > 2.17.1
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