On Tue, Jan 12, 2021 at 6:37 PM Anatoly Burakov
[off-list ref] wrote:

This patchset proposes a simple API for Ethernet drivers to cause the
CPU to enter a power-optimized state while waiting for packets to
arrive. There are multiple proposed mechanisms to achieve said power
savings: simple frequency scaling, idle loop, and monitoring the Rx
queue for incoming packages. The latter is achieved through cooperation
with the NIC driver that will allow us to know address of wake up event,
and wait for writes on that address.

On IA, this is achieved through using UMONITOR/UMWAIT instructions. They
are used in their raw opcode form because there is no widespread
compiler support for them yet. Still, the API is made generic enough to
hopefully support other architectures, if they happen to implement
similar instructions.

To achieve power savings, there is a very simple mechanism used: we're
counting empty polls, and if a certain threshold is reached, we employ
one of the suggested power management schemes automatically, from within
a Rx callback inside the PMD. Once there's traffic again, the empty poll
counter is reset.

This patchset also introduces a few changes into existing power
management-related intrinsics, namely to provide a native way of waking
up a sleeping core without application being responsible for it, as well
as general robustness improvements. There's quite a bit of locking going
on, but these locks are per-thread and very little (if any) contention
is expected, so the performance impact shouldn't be that bad (and in any
case the locking happens when we're about to sleep anyway).

Why are we putting it into ethdev as opposed to leaving this up to the
application? Our customers specifically requested a way to do it with
minimal changes to the application code. The current approach allows to
just flip a switch and automatically have power savings.

Things of note:

- Only 1:1 core to queue mapping is supported, meaning that each lcore
  must at most handle RX on a single queue

If we want to save power, it is likely we would poll more rxqs on a thread.

- Support 3 type policies. Monitor/Pause/Frequency Scaling
- Power management is enabled per-queue
- The API doesn't extend to other device types

v16:
- Implemented Konstantin's suggestions and comments
- Added return values to the API

- This revision breaks SPDK build (reported by UNH):
http://mails.dpdk.org/archives/test-report/2021-January/174069.html


- Build is broken for ARM and PPC at patch:
86491d5bd4 - (HEAD) eal: add monitor wakeup function (25 minutes ago)
<Anatoly Burakov>

Only pasting the ARM failure:
ninja: Entering directory `/home/dmarchan/builds/build-arm64-host-clang'
[1/297] Compiling C object
'lib/76b5a35@@rte_eal@sta/librte_eal_arm_rte_power_intrinsics.c.o'.
FAILED: lib/76b5a35@@rte_eal@sta/librte_eal_arm_rte_power_intrinsics.c.o
aarch64-linux-gnu-gcc -Ilib/76b5a35@@rte_eal@sta -Ilib
-I../../dpdk/lib -I. -I../../dpdk/ -Iconfig -I../../dpdk/config
-Ilib/librte_eal/include -I../../dpdk/lib/librte_eal/include
-Ilib/librte_eal/linux/include
-I../../dpdk/lib/librte_eal/linux/include -Ilib/librte_eal/arm/include
-I../../dpdk/lib/librte_eal/arm/include -Ilib/librte_eal/common
-I../../dpdk/lib/librte_eal/common -Ilib/librte_eal
-I../../dpdk/lib/librte_eal -Ilib/librte_kvargs
-I../../dpdk/lib/librte_kvargs
-Ilib/librte_telemetry/../librte_metrics
-I../../dpdk/lib/librte_telemetry/../librte_metrics
-Ilib/librte_telemetry -I../../dpdk/lib/librte_telemetry
-fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall
-Winvalid-pch -Werror -O2 -g -include rte_config.h -Wextra -Wcast-qual
-Wdeprecated -Wformat -Wformat-nonliteral -Wformat-security
-Wmissing-declarations -Wmissing-prototypes -Wnested-externs
-Wold-style-definition -Wpointer-arith -Wsign-compare
-Wstrict-prototypes -Wundef -Wwrite-strings -Wno-packed-not-aligned
-Wno-missing-field-initializers -D_GNU_SOURCE -fPIC -march=armv8-a+crc
-DALLOW_EXPERIMENTAL_API -DALLOW_INTERNAL_API -Wno-format-truncation
'-DABI_VERSION="21.1"' -DRTE_LIBEAL_USE_GETENTROPY -MD -MQ
'lib/76b5a35@@rte_eal@sta/librte_eal_arm_rte_power_intrinsics.c.o' -MF
'lib/76b5a35@@rte_eal@sta/librte_eal_arm_rte_power_intrinsics.c.o.d'
-o 'lib/76b5a35@@rte_eal@sta/librte_eal_arm_rte_power_intrinsics.c.o'
-c ../../dpdk/lib/librte_eal/arm/rte_power_intrinsics.c
../../dpdk/lib/librte_eal/arm/rte_power_intrinsics.c:35:1: error:
conflicting types for ‘rte_power_monitor_wakeup’
 rte_power_monitor_wakeup(const unsigned int lcore_id)
 ^~~~~~~~~~~~~~~~~~~~~~~~
In file included from
../../dpdk/lib/librte_eal/arm/include/rte_power_intrinsics.h:14,
                 from ../../dpdk/lib/librte_eal/arm/rte_power_intrinsics.c:5:
../../dpdk/lib/librte_eal/include/generic/rte_power_intrinsics.h:79:5:
note: previous declaration of ‘rte_power_monitor_wakeup’ was here
 int rte_power_monitor_wakeup(const unsigned int lcore_id);
     ^~~~~~~~~~~~~~~~~~~~~~~~
ninja: build stopped: subcommand failed.



- The ABI check is still not happy as I reported earlier.
Reproduced on v16 (GHA had a hiccup on this revision, but previous
ones had the failure too):

1 Changed variable:

  [C] 'rte_eth_dev rte_eth_devices[]' was changed at rte_ethdev_core.h:196:1:
    type of variable changed:
      array element type 'struct rte_eth_dev' changed:
        type size hasn't changed
        1 data member change:
          type of 'const eth_dev_ops* rte_eth_dev::dev_ops' changed:
            in pointed to type 'const eth_dev_ops':
              in unqualified underlying type 'struct eth_dev_ops' at
rte_ethdev_driver.h:789:1:
                type size changed from 6208 to 6272 (in bits)
                1 data member insertion:
                  'eth_get_monitor_addr_t
eth_dev_ops::get_monitor_addr', at offset 6208 (in bits) at
rte_ethdev_driver.h:940:1
                no data member changes (94 filtered);
      type size hasn't changed

Error: ABI issue reported for 'abidiff --suppr
/home/dmarchan/dpdk/devtools/../devtools/libabigail.abignore
--no-added-syms --headers-dir1
/home/dmarchan/abi/v20.11/build-gcc-static/usr/local/include
--headers-dir2 /home/dmarchan/builds/build-gcc-static/install/usr/local/include
/home/dmarchan/abi/v20.11/build-gcc-static/dump/librte_ethdev.dump
/home/dmarchan/builds/build-gcc-static/install/dump/librte_ethdev.dump'

ABIDIFF_ABI_CHANGE, this change requires a review (abidiff flagged
this as a potential issue).

One solution is to add an exception on the eth_dev_ops structure.

--- a/devtools/libabigail.abignore
+++ b/devtools/libabigail.abignore

@@ -7,3 +7,7 @@
         symbol_version = INTERNAL
 [suppress_variable]
         symbol_version = INTERNAL
+
+; Explicit ignore for driver-only ABI
+[suppress_type]
+        name = eth_dev_ops

-- 
David marchand