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From: bugzilla@dpdk.org
To: dev@dpdk.org
Subject: [Bug 946] async flow rules affects pmd power management
Date: Wed, 02 Mar 2022 12:27:15 +0000
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https://bugs.dpdk.org/show_bug.cgi?id=3D946

            Bug ID: 946
           Summary: async flow rules affects pmd power management
           Product: DPDK
           Version: unspecified
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: eventdev
          Assignee: dev@dpdk.org
          Reporter: david.hunt@intel.com
  Target Milestone: ---

pmd power management functionality when using RTM transactions never enters
power saving mode.=20

When testing using l3fwd-power to test the power_pmd functionality for DPDK
22.03 rc2, I noticed that the power saved in this DPDK version was
significantly reduced.=20
I tried multiple BIOS/OS/kernel combinations, but then I tried DPDK 21.11,
where the problem went away.=20

I then did a git bisect, which narrowed down the problem to commit
197e820c6685993ad75387de79707c81b5e1fc10 - "ethdev: bring in async queue-ba=
sed
flow rules operations"

The patch has the effect of causing the RTM transaction in
rte_power_monitor_multi(), in the C file lib/eal/x86/rte_power_intrinsics.c=
, to
always fail at rte_xbegin, so we never get to the rte_power_pause, thereby =
we
never get to save any power.=20
If we revert just this patch, then the rte_xbegin succeeds, and we get to c=
all
rte_power_pause, and save power.

So this patch is now causing rte_power_monitor_multi() to fail.=20

I'm not sure what the solution is, but it may be possible to re-work the as=
ync
flow rules patch, or it may be possible to re-work the pmd_power_management
code to avoid the impact of the flow rules patch. Investigation is ongoing.

--=20
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