Hi, Hanoch

Are you talking about i40 VF's latency? And you are using DPDK PF as host 
driver?

In this case, we are setting the Interrupt Throttling (ITR) to be maximum. That 
is to say, if the packet rate is very slow , the receive descriptor is written 
back  when ITR timeout, otherwise it is written back when cache line is full (4 
descriptors/packets). I think that's why you saw the latency is varying.

If we change the ITR to minor, then huge number of interrupts will coming to 
core which impact performance.


Thanks
Jingjing

From: Hanoch Haim (hhaim) [mailto:hh...@cisco.com]
Sent: Friday, November 24, 2017 7:25 PM
To: dev@dpdk.org
Cc: Wu, Jingjing <jingjing...@intel.com>
Subject: RE: [dpdk-dev] net/i40e: latency issue due fix interrupt throttling 
setting in PF

Re-sending

Hanoh

From: Hanoch Haim (hhaim)
Sent: Monday, November 20, 2017 5:19 PM
To: dev@dpdk.org<mailto:dev@dpdk.org>
Cc: Wu, Jingjing (jingjing...@intel.com<mailto:jingjing...@intel.com>); Hanoch 
Haim (hhaim)
Subject: [dpdk-dev] net/i40e: latency issue due fix interrupt throttling 
setting in PF

Hi All,
While integrating dpdk17.11 into TRex latest code a new latency issue is 
observed  (i40e is very sensitive because it has very good resolution due to 
Qos configuration).
git bitsec found the following commit.
With this commit we observe high spikes of Rx latency (~40usec) vs (~8usec).
Any idea why?
I can send how to reproduce this, it is very simple.

cfd662d22e7bddb4ba41dbd1384f8497f38c2b4e is the first bad commit
commit cfd662d22e7bddb4ba41dbd1384f8497f38c2b4e
Author: Jingjing Wu <jingjing...@intel.com<mailto:jingjing...@intel.com>>
Date:   Thu Aug 24 09:57:51 2017 +0800

    net/i40e: fix interrupt throttling setting in PF

    As no matter the PF host driver is DPDK or other kernel drivers,
    they are sharing the same virtchnnl interfaces to communicate to VFs.
    To follow the generic interface, DPDK PF need to set Interrupt
    Throttling (ITR) index according to the rxitr_idx from virtchnnl
    instead of ITR_NONE.

    Fixes: 6d59e4ea74a6 ("net/i40e: change version number to support Linux VF")
    Cc: sta...@dpdk.org<mailto:sta...@dpdk.org>

    Signed-off-by: Jingjing Wu 
<jingjing...@intel.com<mailto:jingjing...@intel.com>>



Thanks,
Hanoh

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