[PATCH v2] mempool: fix get objects from mempool with cache

[Morten Brørup]

@Aaron, do you have any insights or comments to my curiosity below?

> From: Andrew Rybchenko [mailto:andrew.rybchenko at oktetlabs.ru]
> Sent: Tuesday, 4 October 2022 14.58
> 
> Hi Morten,
> 
> In general I agree that the fix is required.
> In sent v3 I'm trying to make it a bit better from my point of
> view. See few notes below.

I stand by my review and accept of v3 - this message is not intended to change that! I'm just curious...

I wonder how accurate the automated performance tests ([v2], [v3]) are, and if they are comparable between February and October?

[v2]: http://mails.dpdk.org/archives/test-report/2022-February/256462.html
[v3]: http://mails.dpdk.org/archives/test-report/2022-October/311526.html


Ubuntu 20.04
Kernel: 4.15.0-generic
Compiler: gcc 7.4
NIC: Intel Corporation Ethernet Converged Network Adapter XL710-QDA2 40000 Mbps
Target: x86_64-native-linuxapp-gcc
Fail/Total: 0/4

Detail performance results:
** V2 **:
+----------+-------------+---------+------------+------------------------------+
| num_cpus | num_threads | txd/rxd | frame_size |  throughput difference from  |
|          |             |         |            |           expected           |
+==========+=============+=========+============+==============================+
| 1        | 2           | 512     | 64         | 0.5%                         |
+----------+-------------+---------+------------+------------------------------+
| 1        | 2           | 2048    | 64         | -1.5%                        |
+----------+-------------+---------+------------+------------------------------+
| 1        | 1           | 512     | 64         | 4.3%                         |
+----------+-------------+---------+------------+------------------------------+
| 1        | 1           | 2048    | 64         | 10.9%                        |
+----------+-------------+---------+------------+------------------------------+

** V3 **:
+----------+-------------+---------+------------+------------------------------+
| num_cpus | num_threads | txd/rxd | frame_size |  throughput difference from  |
|          |             |         |            |           expected           |
+==========+=============+=========+============+==============================+
| 1        | 2           | 512     | 64         | -0.7%                        |
+----------+-------------+---------+------------+------------------------------+
| 1        | 2           | 2048    | 64         | -2.3%                        |
+----------+-------------+---------+------------+------------------------------+
| 1        | 1           | 512     | 64         | 0.5%                         |
+----------+-------------+---------+------------+------------------------------+
| 1        | 1           | 2048    | 64         | 7.9%                         |
+----------+-------------+---------+------------+------------------------------+