On Tue, Sep 30, 2014 at 06:14:46PM +0000, Saha, Avik (AWS) wrote: > I have to point out that I am commenting out the the power_of_2 check on > entry_size. I am not sure if this is the right way but I don't know why this > soft assumption is important (since I cannot find the power of 2 constraint > in the documentation). I agree with the 0 check but the only reason I did not > put that in is because entry size would at least be sizeof(struct > rte_pipeline_table_entry) = 8 bytes (to which the action_data_size is added) > > Avik > I would imagine the power of two check is in place sepcifically because of the zero bit searchs immediately below it. I.e. you can't really create bit masks for multi-field values, when those fields aren't contiguous.
Neil > -----Original Message----- > From: Neil Horman [mailto:nhorman at tuxdriver.com] > Sent: Tuesday, September 30, 2014 5:51 AM > To: Saha, Avik (AWS) > Cc: dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH] Fix for LRU corrupted returns > > On Tue, Sep 30, 2014 at 06:26:23AM +0000, Saha, Avik (AWS) wrote: > > 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. > > > Ah, ok, then change that 32 to sizeof(t->data_size_shl) to protect you > against type changes and to avoid having magic values running around in your > code. Also, you might want to do some sanity checking of entry_size as it > seems like theres a soft assumption that entry size is non-zero and a power > of two. > while the latter is checked higher in the function, the former isn't and > __builtin_clz has undefined behavior if its passed a zero value. > > Neil > > > -----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 > > > > >
