[PATCH] lib/power: power pmd errata with RTM and gcc-9

[PATCH] lib/power: power pmd errata with RTM and gcc-9

[David Hunt]

An errata exists where users may see reduced power savings when using
PMD Power Management. This issue occurs when compiling DPDK applications
with gcc-9 on platforms with TSX enabled. In rte_power_monitor_multi(),
the function may return without successfully starting the RTM
transaction (the _xbegin() fails).

Signed-off-by: David Hunt <david.hunt@intel.com>
---
 doc/guides/rel_notes/release_22_03.rst | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/doc/guides/rel_notes/release_22_03.rst b/doc/guides/rel_notes/release_22_03.rst
index 60e5b4f9aa..34d6f34dba 100644
--- a/doc/guides/rel_notes/release_22_03.rst
+++ b/doc/guides/rel_notes/release_22_03.rst
@@ -313,6 +313,17 @@ Known Issues
    Also, make sure to start the actual text at the margin.
    =======================================================
 
+* **Possible reduced power saving with PMD Power Management.**
+
+  Users may see reduced power savings when using PMD Power Management.
+  This issue occurs when compiling DPDK applications with gcc-9 on
+  platforms with TSX enabled. In rte_power_monitor_multi(), the
+  function may return without successfully starting the RTM
+  transaction (the _xbegin() fails).
+
+  There are three workarounds for this issue. Either build DPDK with gcc-11
+  or newer, build with shared libraries, or build DPDK with fewer drivers.
+
 
 Tested Platforms
 ----------------
-- 
2.17.1

Re: [PATCH] lib/power: power pmd errata with RTM and gcc-9

[Thomas Monjalon]

09/03/2022 14:22, David Hunt:
> An errata exists where users may see reduced power savings when using
> PMD Power Management. This issue occurs when compiling DPDK applications
> with gcc-9 on platforms with TSX enabled. In rte_power_monitor_multi(),
> the function may return without successfully starting the RTM
> transaction (the _xbegin() fails).
> 
> Signed-off-by: David Hunt <david.hunt@intel.com>

Applied, thanks.

Is there a way to fix it or should we keep this errata forever?

Re: [PATCH] lib/power: power pmd errata with RTM and gcc-9

[David Hunt]

On 16/3/2022 7:44 PM, Thomas Monjalon wrote:
> 09/03/2022 14:22, David Hunt:
>> An errata exists where users may see reduced power savings when using
>> PMD Power Management. This issue occurs when compiling DPDK applications
>> with gcc-9 on platforms with TSX enabled. In rte_power_monitor_multi(),
>> the function may return without successfully starting the RTM
>> transaction (the _xbegin() fails).
>>
>> Signed-off-by: David Hunt <david.hunt@intel.com>
> Applied, thanks.
>
> Is there a way to fix it or should we keep this errata forever?


If it's a gcc-9 issue, then we'll have to get the assistance to fix. 
I've send the relevant information on to the gcc folks for analysis, and 
I'll follow up at regular intervals.

I would hope to be able to remove the errata within the next one or two 
releases.