[dpdk-dev] [PATCH] Fix for LRU corrupted returns

[Saha, Avik (AWS)]

Sorry about the delay. The number 32 is not really a CACHE_LINE_SIZE but since __builtin_clz returns the number of leading 0's before the most significant set bit in a 32 bit number (entry_size is uint32_t), I subtract that number from 32 to get the number of trailing bits after the most significant set bit. This will be the separation in my data_mem regions.

-----Original Message-----
From: Neil Horman [mailto:nhorman at tuxdriver.com] 
Sent: Thursday, September 25, 2014 3:22 AM
To: Saha, Avik (AWS)
Cc: dev at dpdk.org
Subject: Re: [dpdk-dev] [PATCH] Fix for LRU corrupted returns

On Thu, Sep 25, 2014 at 07:46:16AM +0000, Saha, Avik (AWS) wrote:
> This is a patch to a problem that I have faced (described in the  thread) and this works for me.
> 
> 1)      Since the data_size_shl was getting its value from the key_size, the table data entries were being corrupted when the calculation to shift the number of bits was being made based on the key_size (according to the document the key_size and entry_size are independently configurable) - With this fix, we get the MSB that is set in entry_size (also removes the constraint of this having to be a power of 2 - not entirely sure if this was the reason the constraint was kept though)
> 2)      The document does not say that the entry_size needs to be a power of 2 and this was failing silently when I was trying to bring my application up.
> 
> diff --git a/DPDK/lib/librte_table/rte_table_hash_lru.c 
> b/DPDK/lib/librte_table/rte_table_hash_lru.c
> index d1a4984..4ec9aa4 100644
> --- a/DPDK/lib/librte_table/rte_table_hash_lru.c
> +++ b/DPDK/lib/librte_table/rte_table_hash_lru.c
> @@ -153,8 +153,10 @@ rte_table_hash_lru_create(void *params, int socket_id, uint32_t entry_size)
>         uint32_t i;
> 
>         /* Check input parameters */
> -       if ((check_params_create(p) != 0) ||
> -               (!rte_is_power_of_2(entry_size)) ||
> +       // Commenting out the power of 2 check on the entry_size since the
> +       // Programmers Guide does not call this out and we are going to handle
> +       // the data_size_shl of the table later on (Line 197)
Please remove the reference to Line 197 here.  Thats not going to remain accurate for very long.

> +       if ((check_params_create(p) != 0) ||
>                 ((sizeof(struct rte_table_hash) % CACHE_LINE_SIZE) != 0) ||
>                 (sizeof(struct bucket) != (CACHE_LINE_SIZE / 2))) {
>                 return NULL;
> @@ -192,7 +194,7 @@ rte_table_hash_lru_create(void *params, int socket_id, uint32_t entry_size)
>         /* Internal */
>         t->bucket_mask = t->n_buckets - 1;
>         t->key_size_shl = __builtin_ctzl(p->key_size);
> -       t->data_size_shl = __builtin_ctzl(p->key_size);
> +       t->data_size_shl = 32 - (__builtin_clz(entry_size));
I presume the 32 value here is a cache line size?  That should be replaced with CACHE_LINE_SIZE...Though looking at it, that doesn't seem sufficient.  Seems like we need a eal abstraction to dynamically tell us what the cache line size is (we can read it from /proc/cpuinfo in linux, not sure about bsd).

Neil