[ovs-dev] [PATCH v2] dpif-netdev: Fix insertion probability

Darrell Ball dball at vmware.com
Fri Jun 23 15:19:43 UTC 2017


Thanks for the V2

Acked-by: Darrell Ball <dlu998 at gmail.com>

On 6/23/17, 8:07 AM, "ovs-dev-bounces at openvswitch.org on behalf of Ciara Loftus" <ovs-dev-bounces at openvswitch.org on behalf of ciara.loftus at intel.com> wrote:

    emc_conditional_insert uses pmd->last_cycles and the packet's RSS hash
    to generate a random number used to determine whether or not an emc
    entry should be inserted. This works for single-packet bursts as
    last_cycles is updated for each burst. However, for bursts > 1 packet,
    where the packets in the batch generate the same RSS hash,
    pmd->last_cycles remains constant for the entire burst also, and thus
    cannot be used as a random number for each packet in the burst.
    
    This commit replaces the use of pmd->last_cycles with random_uint32()
    for this purpose and subsequently fixes the behavior of the
    emc_insert_inv_prob setting for high-throughput (large bursts)
    single-flow cases.
    
    Fixes: 4c30b24602c3 ("dpif-netdev: Conditional EMC insert")
    Reported-by: Kevin Traynor <ktraynor at redhat.com>
    Signed-off-by: Ciara Loftus <ciara.loftus at intel.com>
    ---
    v2:
    - Remove unnecessary ORing in random number calcuation as per Ben's
      suggestion.
    ---
     lib/dpif-netdev.c | 6 +-----
     1 file changed, 1 insertion(+), 5 deletions(-)
    
    diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
    index 4e29085..bf489fc 100644
    --- a/lib/dpif-netdev.c
    +++ b/lib/dpif-netdev.c
    @@ -2073,11 +2073,7 @@ emc_probabilistic_insert(struct dp_netdev_pmd_thread *pmd,
         uint32_t min;
         atomic_read_relaxed(&pmd->dp->emc_insert_min, &min);
     
    -#ifdef DPDK_NETDEV
    -    if (min && (key->hash ^ (uint32_t) pmd->last_cycles) <= min) {
    -#else
    -    if (min && (key->hash ^ random_uint32()) <= min) {
    -#endif
    +    if (min && (random_uint32() <= min)) {
             emc_insert(&pmd->flow_cache, key, flow);
         }
     }
    -- 
    2.4.11
    
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