On 29 Aug 2024, at 10:57, Simon Horman wrote:
> On Tue, Aug 27, 2024 at 11:00:10AM +0200, Eelco Chaudron wrote:
>> It is observed in some environments that there are much more ukeys than
>> actual DP flows. For example:
>>
>> $ ovs-appctl upcall/show
>> system@ovs-system:
>> flows : (current 7) (avg 6) (max 117) (limit 2125)
>> offloaded flows : 525
>> dump duration : 1063ms
>> ufid enabled : true
>>
>> 23: (keys 3612)
>> 24: (keys 3625)
>> 25: (keys 3485)
>>
>> The revalidator threads are busy revalidating the stale ukeys leading to
>> high CPU and long dump duration.
>>
>> This patch tracks the number of consecutive missed dumps. If four dumps
>> are missed in a row, it is assumed that the datapath flow no longer
>> exists, and the ukey can be deleted.
>>
>> Reported-by: Roi Dayan <[email protected]>
>> Co-authored-by: Han Zhou <[email protected]>
>> Co-authored-by: Roi Dayan <[email protected]>
>> Signed-off-by: Han Zhou <[email protected]>
>> Signed-off-by: Roi Dayan <[email protected]>
>> Signed-off-by: Eelco Chaudron <[email protected]>
>> ---
>>
>> v3: - Rewrote fix to use actual dump state, and added a tests case.
>> v4: - Added reason to end of flow_del_reason.
>> - Rather than time based, make it missed dumps based.
>> - Changed it from a TC specific test to a generic unit test.
>> ---
>> ofproto/ofproto-dpif-upcall.c | 18 +++++++++
>> tests/ofproto-dpif.at | 39 ++++++++++++++++++++
>> utilities/usdt-scripts/flow_reval_monitor.py | 4 +-
>> 3 files changed, 60 insertions(+), 1 deletion(-)
>>
>> diff --git a/ofproto/ofproto-dpif-upcall.c b/ofproto/ofproto-dpif-upcall.c
>> index 4d39bc5a7..053cfd863 100644
>> --- a/ofproto/ofproto-dpif-upcall.c
>> +++ b/ofproto/ofproto-dpif-upcall.c
>> @@ -57,6 +57,7 @@ COVERAGE_DEFINE(dumped_inconsistent_flow);
>> COVERAGE_DEFINE(dumped_new_flow);
>> COVERAGE_DEFINE(handler_duplicate_upcall);
>> COVERAGE_DEFINE(revalidate_missed_dp_flow);
>> +COVERAGE_DEFINE(revalidate_missing_dp_flow);
>> COVERAGE_DEFINE(ukey_dp_change);
>> COVERAGE_DEFINE(ukey_invalid_stat_reset);
>> COVERAGE_DEFINE(ukey_replace_contention);
>> @@ -284,6 +285,7 @@ enum flow_del_reason {
>> FDR_TOO_EXPENSIVE, /* Too expensive to revalidate. */
>> FDR_UPDATE_FAIL, /* Datapath update failed. */
>> FDR_XLATION_ERROR, /* Flow translation error. */
>> + FDR_FLOW_MISSING_DP, /* Flow is missing from the datapath. */
>> };
>>
>> /* 'udpif_key's are responsible for tracking the little bit of state udpif
>> @@ -318,6 +320,7 @@ struct udpif_key {
>> uint64_t dump_seq OVS_GUARDED; /* Tracks udpif->dump_seq. */
>> uint64_t reval_seq OVS_GUARDED; /* Tracks udpif->reval_seq. */
>> enum ukey_state state OVS_GUARDED; /* Tracks ukey lifetime. */
>> + uint32_t missed_dumps OVS_GUARDED; /* Missed consecutive dumps.
>> */
>>
>> /* 'state' debug information. */
>> unsigned int state_thread OVS_GUARDED; /* Thread that transitions. */
>> @@ -3040,6 +3043,21 @@ revalidator_sweep__(struct revalidator *revalidator,
>> bool purge)
>> result = revalidate_ukey(udpif, ukey, &stats,
>> &odp_actions,
>> reval_seq, &recircs,
>> &del_reason);
>> }
>
> Hi Eelco,
>
> In practice this probably doesn't make much difference, but it caught my eye.
>
> Is it intentional that the logic below may override
> del_reason and result even in cases where result is
> set to a value other than UKEY_KEEP above (not visible in diff)?
>
> IOW, is it intentional that this reason overrides the others,
> even after work has been done determining the others?
Thanks for reviewing this Simon.
Yes, this is intentional, as there was no straightforward way to incorporate
this check into the if-else-if chain.
I did consider moving this on top of the chain, but than all existing parts
would be indented in the below else chain, which looked messy.
>> +
>> + if (ukey->dump_seq != dump_seq) {
>> + ukey->missed_dumps++;
>> + if (ukey->missed_dumps >= 4) {
>> + /* If the flow was not dumped for 4 revalidator
>> rounds,
>> + * we can assume the datapath flow now longer exists
>> + * and the ukey should be deleted. */
>> + COVERAGE_INC(revalidate_missing_dp_flow);
>> + del_reason = FDR_FLOW_MISSING_DP;
>> + result = UKEY_DELETE;
>> + }
>> + } else {
>> + ukey->missed_dumps = 0;
>> + }
>> +
>> if (result != UKEY_KEEP) {
>> /* Clears 'recircs' if filled by revalidate_ukey(). */
>> reval_op_init(&ops[n_ops++], result, udpif, ukey,
>> &recircs,
>
> ...
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