[ovs-dev] dpif-netdev: Fix double parsing of packets when EMC disabled.
diff mbox series

Message ID 20190311163150.17063-1-i.maximets@samsung.com
State Accepted
Delegated to: Ian Stokes
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Series
  • [ovs-dev] dpif-netdev: Fix double parsing of packets when EMC disabled.
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Commit Message

Ilya Maximets March 11, 2019, 4:31 p.m. UTC
This partially reverts commit bde94613e6276d48a6e0be7a592ebcf9836b4aaf.

Commit bde94613e627 was aimed to slightly ( < 1%) increase performance
in the case where EMC disabled, but it avoids RSS hash calculation and
OVS has to calculate it while executing OVS_ACTION_ATTR_HASH in order
to handle balanced-tcp bonding. At the time of executing that action
there is no parsed flow, and OVS parses the packet for the second time
to calculate the hash. This happens for all packets received from the
virtual interfaces because they have no HW RSS.

Here is the example of 'perf' output for VM --> (bonded PHY) traffic:

  Samples: 401K of event 'cycles', Event count (approx.): 50964771478
  Overhead  Shared Object       Symbol
    27.50%  ovs-vswitchd        [.] dpcls_lookup.370382
    16.30%  ovs-vswitchd        [.] rte_vhost_dequeue_burst.9267
    14.95%  ovs-vswitchd        [.] miniflow_extract
     7.22%  ovs-vswitchd        [.] flow_extract
     7.10%  ovs-vswitchd        [.] dp_netdev_input__.371002.4826
     4.01%  ovs-vswitchd        [.] fast_path_processing.370987.4893

We can see that packet parsed twice. First time by 'miniflow_extract'
right after receiving and the second time by 'flow_extract' while
executing actions.

In this particular case calculating RSS on receive saves > 7% of the
total CPU processing time. It varies from ~7 to ~10 % depending on
scenario/traffic types.

It's better to calculate hash each time because performance
improvements of avoiding are negligible in compare with performance
drop in case of sending packets to bonded interface.

Another solution could be to pass the parsed flow explicitly through
the datapath, but this will require big code changes and will have
additional overhead for metadata updating on packet changes.

Also, this change should have small impact since SMC works well in most
cases and will be enabled/recommended by default in the future.

CC: Antonio Fischetti <antonio.fischetti@intel.com>
Fixes: bde94613e627 ("dpif-netdev: Avoid reading RSS hash when EMC is disabled.")
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
---
 lib/dpif-netdev.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

Comments

Ilya Maximets April 18, 2019, 7:55 a.m. UTC | #1
On 11.03.2019 19:31, Ilya Maximets wrote:
> This partially reverts commit bde94613e6276d48a6e0be7a592ebcf9836b4aaf.
> 
> Commit bde94613e627 was aimed to slightly ( < 1%) increase performance
> in the case where EMC disabled, but it avoids RSS hash calculation and
> OVS has to calculate it while executing OVS_ACTION_ATTR_HASH in order
> to handle balanced-tcp bonding. At the time of executing that action
> there is no parsed flow, and OVS parses the packet for the second time
> to calculate the hash. This happens for all packets received from the
> virtual interfaces because they have no HW RSS.
> 
> Here is the example of 'perf' output for VM --> (bonded PHY) traffic:
> 
>   Samples: 401K of event 'cycles', Event count (approx.): 50964771478
>   Overhead  Shared Object       Symbol
>     27.50%  ovs-vswitchd        [.] dpcls_lookup.370382
>     16.30%  ovs-vswitchd        [.] rte_vhost_dequeue_burst.9267
>     14.95%  ovs-vswitchd        [.] miniflow_extract
>      7.22%  ovs-vswitchd        [.] flow_extract
>      7.10%  ovs-vswitchd        [.] dp_netdev_input__.371002.4826
>      4.01%  ovs-vswitchd        [.] fast_path_processing.370987.4893
> 
> We can see that packet parsed twice. First time by 'miniflow_extract'
> right after receiving and the second time by 'flow_extract' while
> executing actions.
> 
> In this particular case calculating RSS on receive saves > 7% of the
> total CPU processing time. It varies from ~7 to ~10 % depending on
> scenario/traffic types.
> 
> It's better to calculate hash each time because performance
> improvements of avoiding are negligible in compare with performance
> drop in case of sending packets to bonded interface.
> 
> Another solution could be to pass the parsed flow explicitly through
> the datapath, but this will require big code changes and will have
> additional overhead for metadata updating on packet changes.
> 
> Also, this change should have small impact since SMC works well in most
> cases and will be enabled/recommended by default in the future.
> 
> CC: Antonio Fischetti <antonio.fischetti@intel.com>
> Fixes: bde94613e627 ("dpif-netdev: Avoid reading RSS hash when EMC is disabled.")
> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> ---

Hi.
Any thoughts about this patch?
This is a big performance issue on setups with OVS bonding.

Best regards, Ilya Maximets.

>  lib/dpif-netdev.c | 21 +++++++--------------
>  1 file changed, 7 insertions(+), 14 deletions(-)
> 
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 4d6d0c372..35cd00712 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -6438,20 +6438,13 @@ dfc_processing(struct dp_netdev_pmd_thread *pmd,
>  
>          miniflow_extract(packet, &key->mf);
>          key->len = 0; /* Not computed yet. */
> -        /* If EMC and SMC disabled skip hash computation */
> -        if (smc_enable_db == true || cur_min != 0) {
> -            if (!md_is_valid) {
> -                key->hash = dpif_netdev_packet_get_rss_hash_orig_pkt(packet,
> -                        &key->mf);
> -            } else {
> -                key->hash = dpif_netdev_packet_get_rss_hash(packet, &key->mf);
> -            }
> -        }
> -        if (cur_min) {
> -            flow = emc_lookup(&cache->emc_cache, key);
> -        } else {
> -            flow = NULL;
> -        }
> +        key->hash =
> +                (md_is_valid == false)
> +                ? dpif_netdev_packet_get_rss_hash_orig_pkt(packet, &key->mf)
> +                : dpif_netdev_packet_get_rss_hash(packet, &key->mf);
> +
> +        /* If EMC is disabled skip emc_lookup */
> +        flow = (cur_min != 0) ? emc_lookup(&cache->emc_cache, key) : NULL;
>          if (OVS_LIKELY(flow)) {
>              tcp_flags = miniflow_get_tcp_flags(&key->mf);
>              n_emc_hit++;
>
Ian Stokes April 18, 2019, 8:08 a.m. UTC | #2
On 4/18/2019 8:55 AM, Ilya Maximets wrote:
> On 11.03.2019 19:31, Ilya Maximets wrote:
>> This partially reverts commit bde94613e6276d48a6e0be7a592ebcf9836b4aaf.
>>
>> Commit bde94613e627 was aimed to slightly ( < 1%) increase performance
>> in the case where EMC disabled, but it avoids RSS hash calculation and
>> OVS has to calculate it while executing OVS_ACTION_ATTR_HASH in order
>> to handle balanced-tcp bonding. At the time of executing that action
>> there is no parsed flow, and OVS parses the packet for the second time
>> to calculate the hash. This happens for all packets received from the
>> virtual interfaces because they have no HW RSS.
>>
>> Here is the example of 'perf' output for VM --> (bonded PHY) traffic:
>>
>>    Samples: 401K of event 'cycles', Event count (approx.): 50964771478
>>    Overhead  Shared Object       Symbol
>>      27.50%  ovs-vswitchd        [.] dpcls_lookup.370382
>>      16.30%  ovs-vswitchd        [.] rte_vhost_dequeue_burst.9267
>>      14.95%  ovs-vswitchd        [.] miniflow_extract
>>       7.22%  ovs-vswitchd        [.] flow_extract
>>       7.10%  ovs-vswitchd        [.] dp_netdev_input__.371002.4826
>>       4.01%  ovs-vswitchd        [.] fast_path_processing.370987.4893
>>
>> We can see that packet parsed twice. First time by 'miniflow_extract'
>> right after receiving and the second time by 'flow_extract' while
>> executing actions.
>>
>> In this particular case calculating RSS on receive saves > 7% of the
>> total CPU processing time. It varies from ~7 to ~10 % depending on
>> scenario/traffic types.
>>
>> It's better to calculate hash each time because performance
>> improvements of avoiding are negligible in compare with performance
>> drop in case of sending packets to bonded interface.
>>
>> Another solution could be to pass the parsed flow explicitly through
>> the datapath, but this will require big code changes and will have
>> additional overhead for metadata updating on packet changes.
>>
>> Also, this change should have small impact since SMC works well in most
>> cases and will be enabled/recommended by default in the future.
>>
>> CC: Antonio Fischetti <antonio.fischetti@intel.com>
>> Fixes: bde94613e627 ("dpif-netdev: Avoid reading RSS hash when EMC is disabled.")
>> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
>> ---
> 
> Hi.
> Any thoughts about this patch?
> This is a big performance issue on setups with OVS bonding.
> 

Hi Ilya,

I'm just finishing up performance testing I started yesterday with this 
patch, I'm inclined to agree with you.

 From bench marking with master I see the following with EMC disabled 
with RFC2544 (0% packet loss).

(Master - No hash when EMC disabled)
Packet Size	RX Rate PPs	RX Rate Mbps	RX %
64		6824334.554	3494.059	45.859
128		6878122.822	7043.198	81.438
256		4528973.86	9275.338	100
512		2349613.015	9624.015	100
1024		1197312.023	9808.38		100
1500		822368.143	9868.418	100

With the revert applied I see

(Patch - hash applied when EMC disabled)
Packet Size	RX Rate PPs	RX Rate Mbps	RX %
64		6479041.962	3317.269	43.539
128		6747525.93	6909.467	79.891
256		4528894.363	9275.176	100
512		2349615.976	9624.027	100
1024		1197313.173	9808.39		100
1500		822365.834	9868.39		100

So the gain for avoiding the hash is marginal and certainly not equal to 
the gain achieved when enabled with bonding as you reported.

Even testing with scaling high number of flows there is a similar pattern.

(Master - No hash when EMC disabled)
Packet Size	RX Rate PPs	RX Rate Mbps	RX %
64		13418452.15	6870.248	45.086

(Patch - hash applied when EMC disabled)	
Packet Size	RX Rate PPs	RX Rate Mbps	RX %
64		12958087.12	6634.541	43.539
			
With this in mind I'll push this to master today.

Ian

> Best regards, Ilya Maximets.
> 
>>   lib/dpif-netdev.c | 21 +++++++--------------
>>   1 file changed, 7 insertions(+), 14 deletions(-)
>>
>> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
>> index 4d6d0c372..35cd00712 100644
>> --- a/lib/dpif-netdev.c
>> +++ b/lib/dpif-netdev.c
>> @@ -6438,20 +6438,13 @@ dfc_processing(struct dp_netdev_pmd_thread *pmd,
>>   
>>           miniflow_extract(packet, &key->mf);
>>           key->len = 0; /* Not computed yet. */
>> -        /* If EMC and SMC disabled skip hash computation */
>> -        if (smc_enable_db == true || cur_min != 0) {
>> -            if (!md_is_valid) {
>> -                key->hash = dpif_netdev_packet_get_rss_hash_orig_pkt(packet,
>> -                        &key->mf);
>> -            } else {
>> -                key->hash = dpif_netdev_packet_get_rss_hash(packet, &key->mf);
>> -            }
>> -        }
>> -        if (cur_min) {
>> -            flow = emc_lookup(&cache->emc_cache, key);
>> -        } else {
>> -            flow = NULL;
>> -        }
>> +        key->hash =
>> +                (md_is_valid == false)
>> +                ? dpif_netdev_packet_get_rss_hash_orig_pkt(packet, &key->mf)
>> +                : dpif_netdev_packet_get_rss_hash(packet, &key->mf);
>> +
>> +        /* If EMC is disabled skip emc_lookup */
>> +        flow = (cur_min != 0) ? emc_lookup(&cache->emc_cache, key) : NULL;
>>           if (OVS_LIKELY(flow)) {
>>               tcp_flags = miniflow_get_tcp_flags(&key->mf);
>>               n_emc_hit++;
>>
Ilya Maximets April 18, 2019, 12:43 p.m. UTC | #3
On 18.04.2019 11:08, Ian Stokes wrote:
> On 4/18/2019 8:55 AM, Ilya Maximets wrote:
>> On 11.03.2019 19:31, Ilya Maximets wrote:
>>> This partially reverts commit bde94613e6276d48a6e0be7a592ebcf9836b4aaf.
>>>
>>> Commit bde94613e627 was aimed to slightly ( < 1%) increase performance
>>> in the case where EMC disabled, but it avoids RSS hash calculation and
>>> OVS has to calculate it while executing OVS_ACTION_ATTR_HASH in order
>>> to handle balanced-tcp bonding. At the time of executing that action
>>> there is no parsed flow, and OVS parses the packet for the second time
>>> to calculate the hash. This happens for all packets received from the
>>> virtual interfaces because they have no HW RSS.
>>>
>>> Here is the example of 'perf' output for VM --> (bonded PHY) traffic:
>>>
>>>    Samples: 401K of event 'cycles', Event count (approx.): 50964771478
>>>    Overhead  Shared Object       Symbol
>>>      27.50%  ovs-vswitchd        [.] dpcls_lookup.370382
>>>      16.30%  ovs-vswitchd        [.] rte_vhost_dequeue_burst.9267
>>>      14.95%  ovs-vswitchd        [.] miniflow_extract
>>>       7.22%  ovs-vswitchd        [.] flow_extract
>>>       7.10%  ovs-vswitchd        [.] dp_netdev_input__.371002.4826
>>>       4.01%  ovs-vswitchd        [.] fast_path_processing.370987.4893
>>>
>>> We can see that packet parsed twice. First time by 'miniflow_extract'
>>> right after receiving and the second time by 'flow_extract' while
>>> executing actions.
>>>
>>> In this particular case calculating RSS on receive saves > 7% of the
>>> total CPU processing time. It varies from ~7 to ~10 % depending on
>>> scenario/traffic types.
>>>
>>> It's better to calculate hash each time because performance
>>> improvements of avoiding are negligible in compare with performance
>>> drop in case of sending packets to bonded interface.
>>>
>>> Another solution could be to pass the parsed flow explicitly through
>>> the datapath, but this will require big code changes and will have
>>> additional overhead for metadata updating on packet changes.
>>>
>>> Also, this change should have small impact since SMC works well in most
>>> cases and will be enabled/recommended by default in the future.
>>>
>>> CC: Antonio Fischetti <antonio.fischetti@intel.com>
>>> Fixes: bde94613e627 ("dpif-netdev: Avoid reading RSS hash when EMC is disabled.")
>>> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
>>> ---
>>
>> Hi.
>> Any thoughts about this patch?
>> This is a big performance issue on setups with OVS bonding.
>>
> 
> Hi Ilya,
> 
> I'm just finishing up performance testing I started yesterday with this patch, I'm inclined to agree with you.
> 
> From bench marking with master I see the following with EMC disabled with RFC2544 (0% packet loss).
> 
> (Master - No hash when EMC disabled)
> Packet Size    RX Rate PPs    RX Rate Mbps    RX %
> 64        6824334.554    3494.059    45.859
> 128        6878122.822    7043.198    81.438
> 256        4528973.86    9275.338    100
> 512        2349613.015    9624.015    100
> 1024        1197312.023    9808.38        100
> 1500        822368.143    9868.418    100
> 
> With the revert applied I see
> 
> (Patch - hash applied when EMC disabled)
> Packet Size    RX Rate PPs    RX Rate Mbps    RX %
> 64        6479041.962    3317.269    43.539
> 128        6747525.93    6909.467    79.891
> 256        4528894.363    9275.176    100
> 512        2349615.976    9624.027    100
> 1024        1197313.173    9808.39        100
> 1500        822365.834    9868.39        100
> 
> So the gain for avoiding the hash is marginal and certainly not equal to the gain achieved when enabled with bonding as you reported.
> 
> Even testing with scaling high number of flows there is a similar pattern.
> 
> (Master - No hash when EMC disabled)
> Packet Size    RX Rate PPs    RX Rate Mbps    RX %
> 64        13418452.15    6870.248    45.086
> 
> (Patch - hash applied when EMC disabled)   
> Packet Size    RX Rate PPs    RX Rate Mbps    RX %
> 64        12958087.12    6634.541    43.539
>            
> With this in mind I'll push this to master today.

Thanks for testing and applying.

What about backporting? The issue affects all branches since 2.9.
Applies cleanly down to 2.10. I could send separate patch for 2.9
if needed.


> 
> Ian
> 
>> Best regards, Ilya Maximets.
>>
>>>   lib/dpif-netdev.c | 21 +++++++--------------
>>>   1 file changed, 7 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
>>> index 4d6d0c372..35cd00712 100644
>>> --- a/lib/dpif-netdev.c
>>> +++ b/lib/dpif-netdev.c
>>> @@ -6438,20 +6438,13 @@ dfc_processing(struct dp_netdev_pmd_thread *pmd,
>>>             miniflow_extract(packet, &key->mf);
>>>           key->len = 0; /* Not computed yet. */
>>> -        /* If EMC and SMC disabled skip hash computation */
>>> -        if (smc_enable_db == true || cur_min != 0) {
>>> -            if (!md_is_valid) {
>>> -                key->hash = dpif_netdev_packet_get_rss_hash_orig_pkt(packet,
>>> -                        &key->mf);
>>> -            } else {
>>> -                key->hash = dpif_netdev_packet_get_rss_hash(packet, &key->mf);
>>> -            }
>>> -        }
>>> -        if (cur_min) {
>>> -            flow = emc_lookup(&cache->emc_cache, key);
>>> -        } else {
>>> -            flow = NULL;
>>> -        }
>>> +        key->hash =
>>> +                (md_is_valid == false)
>>> +                ? dpif_netdev_packet_get_rss_hash_orig_pkt(packet, &key->mf)
>>> +                : dpif_netdev_packet_get_rss_hash(packet, &key->mf);
>>> +
>>> +        /* If EMC is disabled skip emc_lookup */
>>> +        flow = (cur_min != 0) ? emc_lookup(&cache->emc_cache, key) : NULL;
>>>           if (OVS_LIKELY(flow)) {
>>>               tcp_flags = miniflow_get_tcp_flags(&key->mf);
>>>               n_emc_hit++;
>>>
> 
> 
>
Ian Stokes April 18, 2019, 3:58 p.m. UTC | #4
On 4/18/2019 1:43 PM, Ilya Maximets wrote:
> 
> 
> On 18.04.2019 11:08, Ian Stokes wrote:
>> On 4/18/2019 8:55 AM, Ilya Maximets wrote:
>>> On 11.03.2019 19:31, Ilya Maximets wrote:
>>>> This partially reverts commit bde94613e6276d48a6e0be7a592ebcf9836b4aaf.
>>>>
>>>> Commit bde94613e627 was aimed to slightly ( < 1%) increase performance
>>>> in the case where EMC disabled, but it avoids RSS hash calculation and
>>>> OVS has to calculate it while executing OVS_ACTION_ATTR_HASH in order
>>>> to handle balanced-tcp bonding. At the time of executing that action
>>>> there is no parsed flow, and OVS parses the packet for the second time
>>>> to calculate the hash. This happens for all packets received from the
>>>> virtual interfaces because they have no HW RSS.
>>>>
>>>> Here is the example of 'perf' output for VM --> (bonded PHY) traffic:
>>>>
>>>>     Samples: 401K of event 'cycles', Event count (approx.): 50964771478
>>>>     Overhead  Shared Object       Symbol
>>>>       27.50%  ovs-vswitchd        [.] dpcls_lookup.370382
>>>>       16.30%  ovs-vswitchd        [.] rte_vhost_dequeue_burst.9267
>>>>       14.95%  ovs-vswitchd        [.] miniflow_extract
>>>>        7.22%  ovs-vswitchd        [.] flow_extract
>>>>        7.10%  ovs-vswitchd        [.] dp_netdev_input__.371002.4826
>>>>        4.01%  ovs-vswitchd        [.] fast_path_processing.370987.4893
>>>>
>>>> We can see that packet parsed twice. First time by 'miniflow_extract'
>>>> right after receiving and the second time by 'flow_extract' while
>>>> executing actions.
>>>>
>>>> In this particular case calculating RSS on receive saves > 7% of the
>>>> total CPU processing time. It varies from ~7 to ~10 % depending on
>>>> scenario/traffic types.
>>>>
>>>> It's better to calculate hash each time because performance
>>>> improvements of avoiding are negligible in compare with performance
>>>> drop in case of sending packets to bonded interface.
>>>>
>>>> Another solution could be to pass the parsed flow explicitly through
>>>> the datapath, but this will require big code changes and will have
>>>> additional overhead for metadata updating on packet changes.
>>>>
>>>> Also, this change should have small impact since SMC works well in most
>>>> cases and will be enabled/recommended by default in the future.
>>>>
>>>> CC: Antonio Fischetti <antonio.fischetti@intel.com>
>>>> Fixes: bde94613e627 ("dpif-netdev: Avoid reading RSS hash when EMC is disabled.")
>>>> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
>>>> ---
>>>
>>> Hi.
>>> Any thoughts about this patch?
>>> This is a big performance issue on setups with OVS bonding.
>>>
>>
>> Hi Ilya,
>>
>> I'm just finishing up performance testing I started yesterday with this patch, I'm inclined to agree with you.
>>
>>  From bench marking with master I see the following with EMC disabled with RFC2544 (0% packet loss).
>>
>> (Master - No hash when EMC disabled)
>> Packet Size    RX Rate PPs    RX Rate Mbps    RX %
>> 64        6824334.554    3494.059    45.859
>> 128        6878122.822    7043.198    81.438
>> 256        4528973.86    9275.338    100
>> 512        2349613.015    9624.015    100
>> 1024        1197312.023    9808.38        100
>> 1500        822368.143    9868.418    100
>>
>> With the revert applied I see
>>
>> (Patch - hash applied when EMC disabled)
>> Packet Size    RX Rate PPs    RX Rate Mbps    RX %
>> 64        6479041.962    3317.269    43.539
>> 128        6747525.93    6909.467    79.891
>> 256        4528894.363    9275.176    100
>> 512        2349615.976    9624.027    100
>> 1024        1197313.173    9808.39        100
>> 1500        822365.834    9868.39        100
>>
>> So the gain for avoiding the hash is marginal and certainly not equal to the gain achieved when enabled with bonding as you reported.
>>
>> Even testing with scaling high number of flows there is a similar pattern.
>>
>> (Master - No hash when EMC disabled)
>> Packet Size    RX Rate PPs    RX Rate Mbps    RX %
>> 64        13418452.15    6870.248    45.086
>>
>> (Patch - hash applied when EMC disabled)
>> Packet Size    RX Rate PPs    RX Rate Mbps    RX %
>> 64        12958087.12    6634.541    43.539
>>             
>> With this in mind I'll push this to master today.
> 
> Thanks for testing and applying.
> 
> What about backporting? The issue affects all branches since 2.9.
> Applies cleanly down to 2.10. I could send separate patch for 2.9
> if needed.
> 

Yes, good point, I've pushed 2.11, 2.10. and a reworked patch for 2.9.

Thanks
Ian

Patch
diff mbox series

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 4d6d0c372..35cd00712 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -6438,20 +6438,13 @@  dfc_processing(struct dp_netdev_pmd_thread *pmd,
 
         miniflow_extract(packet, &key->mf);
         key->len = 0; /* Not computed yet. */
-        /* If EMC and SMC disabled skip hash computation */
-        if (smc_enable_db == true || cur_min != 0) {
-            if (!md_is_valid) {
-                key->hash = dpif_netdev_packet_get_rss_hash_orig_pkt(packet,
-                        &key->mf);
-            } else {
-                key->hash = dpif_netdev_packet_get_rss_hash(packet, &key->mf);
-            }
-        }
-        if (cur_min) {
-            flow = emc_lookup(&cache->emc_cache, key);
-        } else {
-            flow = NULL;
-        }
+        key->hash =
+                (md_is_valid == false)
+                ? dpif_netdev_packet_get_rss_hash_orig_pkt(packet, &key->mf)
+                : dpif_netdev_packet_get_rss_hash(packet, &key->mf);
+
+        /* If EMC is disabled skip emc_lookup */
+        flow = (cur_min != 0) ? emc_lookup(&cache->emc_cache, key) : NULL;
         if (OVS_LIKELY(flow)) {
             tcp_flags = miniflow_get_tcp_flags(&key->mf);
             n_emc_hit++;