Hi, Cristian > -----Original Message----- > From: Dumitrescu, Cristian <cristian.dumitre...@intel.com> > Sent: Monday, July 20, 2020 10:38 PM > To: Xu, Ting <ting...@intel.com>; dev@dpdk.org > Cc: sta...@dpdk.org > Subject: RE: [PATCH v3] lib/table: fix cache alignment issue > > > > > -----Original Message----- > > From: Xu, Ting <ting...@intel.com> > > Sent: Thursday, July 9, 2020 2:48 AM > > To: dev@dpdk.org > > Cc: Dumitrescu, Cristian <cristian.dumitre...@intel.com>; Xu, Ting > > <ting...@intel.com>; sta...@dpdk.org > > Subject: [PATCH v3] lib/table: fix cache alignment issue > > > > When create softnic hash table with 16 keys, it failed on 32bit > > environment because of the structure rte_bucket_4_16 alignment issue. > > Add __rte_cache_aligned to ensure correct cache align. > > > > Fixes: 8aa327214c ("table: hash") > > Cc: sta...@dpdk.org > > > > Signed-off-by: Ting Xu <ting...@intel.com> > > > > --- > > v2->v3: Rebase > > v1->v2: Correct patch time > > --- > > lib/librte_table/rte_table_hash_key16.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/lib/librte_table/rte_table_hash_key16.c > > b/lib/librte_table/rte_table_hash_key16.c > > index 2cca1c924..5e1665c15 100644 > > --- a/lib/librte_table/rte_table_hash_key16.c > > +++ b/lib/librte_table/rte_table_hash_key16.c > > @@ -44,7 +44,7 @@ struct rte_bucket_4_16 { > > uint64_t key[4][2]; > > > > /* Cache line 2 */ > > - uint8_t data[0]; > > + uint8_t data[0] __rte_cache_aligned; > > }; > > > > struct rte_table_hash { > > -- > > 2.17.1 > > Hi Ting, > > This fix is breaking the execution for systems with cache line of 128 bytes, > as > typically (on 64-bit systems) this structure would be 64-byte in size and > adding the __rte_cache_aligned would force doubling the size of this > structure through padding enforced by the compiler. > > Can you please confirm this is caused by check below failing in the table > create function: > sizeof(struct rte_bucket_4_16) % 64) != 0 >
The result of sizeof(struct rte_bucket_4_16) is 124 byte in this case, and this is the direct reason causing this failure. > Since all the other fields in this data structure are explicitly declared as > 64-bit > fields, due to the alignment rules I was expecting the compiler to add a > 32-bit > padding field after the "next" field, which is a pointer that would only take > 32 > bits on 32-bit systems. I am not sure why this did not take place in your > case, > any thoughts? > It shows that the size of the field struct rte_bucket_4_16 *next in struct rte_bucket_4_16 is only 32 bits. And there is no padding added by the compiler in my and the reporter's case. I tried to add a 32 bits pad field after the field next manually, and the result is correct then. Is it because in 32-bit system, the compiler will not extend the 32 bits pointer to 64 bits, since the 32 bits size has already matched the cache line? > Not sure why we would run Soft NIC on 32-bit systems, might be better to > disable Soft NIC for 32-bit systems. > To be honest, I do not know why we should run softnic on 32-bit system, I was just assigned this specific bug. It seems there is a complete test case for validation team to test softnic in 32-bit system. I am not sure is it OK to tell the validation team that we should disable softnic in 32-bit system now. Or we should fix this issue this time and discuss about the problem later? Thanks! > Thanks, > Cristian