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In-Reply-To: <20200722021628.17194-1-ting.xu@intel.com>
From: David Marchand <david.marchand@redhat.com>
Date: Wed, 29 Jul 2020 14:01:25 +0200
Message-ID: <CAJFAV8zZRQEjVGp07NzuraHuA9YWWK_6VZZ5hN69w2GQuFeTeQ@mail.gmail.com>
To: Ting Xu <ting.xu@intel.com>,
Cristian Dumitrescu <cristian.dumitrescu@intel.com>
Cc: dev <dev@dpdk.org>, dpdk stable <stable@dpdk.org>
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Subject: Re: [dpdk-dev] [PATCH v4] lib/table: fix cache alignment issue
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On Wed, Jul 22, 2020 at 4:13 AM Ting Xu <ting.xu@intel.com> wrote:
>
> When create softnic hash table with 16 keys, it failed on 32-bit
> environment, because the pointer field in structure rte_bucket_4_16
> is only 32 bits. Add a padding field in 32-bit environment to keep
> the structure to a multiple of 64 bytes. Apply this to 8-byte and
> 32-byte key hash function as well.
Please correct me if I am wrong, but it simply means this part of the
table library never worked for 32-bit.
It seems more adding 32-bit support rather than a fix and then I
wonder if it has its place in rc3.
Now, looking at the details:
For 64-bit on my x86, we have:
struct rte_bucket_4_8 {
uint64_t signature; /* 0 8 */
uint64_t lru_list; /* 8 8 */
struct rte_bucket_4_8 * next; /* 16 8 */
uint64_t next_valid; /* 24 8 */
uint64_t key[4]; /* 32 32 */
/* --- cacheline 1 boundary (64 bytes) --- */
uint8_t data[]; /* 64 0 */
/* size: 64, cachelines: 1, members: 6 */
};
For 32-bit, we have:
struct rte_bucket_4_8 {
uint64_t signature; /* 0 8 */
uint64_t lru_list; /* 8 8 */
struct rte_bucket_4_8 * next; /* 16 4 */
uint64_t next_valid; /* 20 8 */
uint64_t key[4]; /* 28 32 */
uint8_t data[]; /* 60 0 */
/* size: 60, cachelines: 1, members: 6 */
/* last cacheline: 60 bytes */
} __attribute__((__packed__));
^^ it is interesting that a packed attribute ends up here.
I saw no such attribute in the library code.
Compiler black magic at work I guess...
>
> Fixes: 8aa327214c ("table: hash")
> Cc: stable@dpdk.org
>
> Signed-off-by: Ting Xu <ting.xu@intel.com>
>
> ---
> v3->v4: Change design based on comment
> v2->v3: Rebase
> v1->v2: Correct patch time
> ---
> lib/librte_table/rte_table_hash_key16.c | 17 +++++++++++++++++
> lib/librte_table/rte_table_hash_key32.c | 17 +++++++++++++++++
> lib/librte_table/rte_table_hash_key8.c | 16 ++++++++++++++++
> 3 files changed, 50 insertions(+)
>
> diff --git a/lib/librte_table/rte_table_hash_key16.c b/lib/librte_table/rte_table_hash_key16.c
> index 2cca1c924..c4384b114 100644
> --- a/lib/librte_table/rte_table_hash_key16.c
> +++ b/lib/librte_table/rte_table_hash_key16.c
> @@ -33,6 +33,7 @@
>
> #endif
>
> +#ifdef RTE_ARCH_64
> struct rte_bucket_4_16 {
> /* Cache line 0 */
> uint64_t signature[4 + 1];
> @@ -46,6 +47,22 @@ struct rte_bucket_4_16 {
> /* Cache line 2 */
> uint8_t data[0];
> };
> +#else
> +struct rte_bucket_4_16 {
> + /* Cache line 0 */
> + uint64_t signature[4 + 1];
> + uint64_t lru_list;
> + struct rte_bucket_4_16 *next;
> + uint32_t pad;
> + uint64_t next_valid;
> +
> + /* Cache line 1 */
> + uint64_t key[4][2];
> +
> + /* Cache line 2 */
> + uint8_t data[0];
> +};
> +#endif
The change could simply be:
@@ -38,6 +38,9 @@ struct rte_bucket_4_16 {
uint64_t signature[4 + 1];
uint64_t lru_list;
struct rte_bucket_4_16 *next;
+#ifndef RTE_ARCH_64
+ uint32_t pad;
+#endif
uint64_t next_valid;
/* Cache line 1 */
It avoids duplicating the whole structure definition (we could miss
updating one side of the #ifdef later).
Idem for the other "8" and "32" structures.
--
David Marchand