[v8,0/6] use WFE for aarch64
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Message ID 1571651279-51857-1-git-send-email-gavin.hu@arm.com
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  • use WFE for aarch64
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Gavin Hu Oct. 21, 2019, 9:47 a.m. UTC
V8:
- define wfe() and sev() macros and use them inside normal C code (Ananyev Konstantin)
- pass memorder as parameter, not to incorporate it into function name, less functions, similar to C11 atomic intrinsics (Ananyev Konstantin)
- remove mandating RTE_FORCE_INTRINSICS in arm spinlock implementation(David Marchand)
- undef __WAIT_UNTIL_EQUAL after use (David Marchand)
- add experimental tag and warning (David Marchand)
- add the limitation of using WFE instruction in the commit log (David Marchand) 
- tweak the use of RTE_FORCE_INSTRINSICS(still mandatory for aarch64) and RTE_ARM_USE_WFE for spinlock (David Marchand)
- drop the rte_ring patch from this series, as the rte_ring.h calls this API and it is widely included by a lot of components each requires the ALLOW_EXPERIMENRAL_API for the Makefile and meson.build, leave it to future after the experimental is removed.
V7:
- fix the checkpatch LONG_LINE_COMMENT issue
V6:
- squash the RTE_ARM_USE_WFE configuration entry patch into the new API patch
- move the new configuration to the end of EAL
- add doxygen comments to reflect the relaxed and acquire semantics
- correct the meson configuration 
V5:
- add doxygen comments for the new APIs
- spinlock early exit without wfe if the spinlock not taken by others.
- add two patches on top for opdl and thunderx
V4:
- rename the config as CONFIG_RTE_ARM_USE_WFE to indicate it applys to arm only
- introduce a macro for assembly Skelton to reduce the duplication of code
- add one patch for nxp fslmc to address a compiling error
V3:
- Convert RFCs to patches
V2:
- Use inline functions instead of marcos
- Add load and compare in the beginning of the APIs
- Fix some style errors in asm inline 
V1:
- Add the new APIs and use it for ring and locks

DPDK has multiple use cases where the core repeatedly polls a location in
memory. This polling results in many cache and memory transactions.

Arm architecture provides WFE (Wait For Event) instruction, which allows
the cpu core to enter a low power state until woken up by the update to the
memory location being polled. Thus reducing the cache and memory
transactions.

x86 has the PAUSE hint instruction to reduce such overhead.

The rte_wait_until_equal_xxx APIs abstract the functionality of 'polling
for a memory location to become equal to a given value'.

For non-Arm platforms, these APIs are just wrappers around do-while loop
with rte_pause, so there are no performance differences.

For Arm platforms, use of WFE can be configured using CONFIG_RTE_USE_WFE
option. It is disabled by default.

Currently, use of WFE is supported only for aarch64 platforms. armv7
platforms do support the WFE instruction, but they require explicit wake up
events(sev) and are less performannt.

Testing shows that, performance varies across different platforms, with
some showing degradation.

CONFIG_RTE_ARM_USE_WFE should be enabled depending on the performance
benchmarking on the target platforms. Power saving should be an bonus,
but currenly we don't have ways to characterize that.

Gavin Hu (6):
  bus/fslmc: fix the conflicting dmb function
  eal: add the APIs to wait until equal
  spinlock: use wfe to reduce contention on aarch64
  ticketlock: use new API to reduce contention on aarch64
  net/thunderx: use new API to save cycles on aarch64
  event/opdl: use new API to save cycles on aarch64

 config/arm/meson.build                             |  1 +
 config/common_base                                 |  5 ++
 drivers/bus/fslmc/mc/fsl_mc_sys.h                  |  8 +-
 drivers/event/opdl/Makefile                        |  1 +
 drivers/event/opdl/meson.build                     |  1 +
 drivers/event/opdl/opdl_ring.c                     |  5 +-
 drivers/net/thunderx/Makefile                      |  1 +
 drivers/net/thunderx/meson.build                   |  1 +
 drivers/net/thunderx/nicvf_rxtx.c                  |  3 +-
 .../common/include/arch/arm/rte_pause_64.h         | 26 ++++++
 .../common/include/arch/arm/rte_spinlock.h         | 26 ++++++
 lib/librte_eal/common/include/generic/rte_pause.h  | 93 ++++++++++++++++++++++
 .../common/include/generic/rte_spinlock.h          |  2 +-
 .../common/include/generic/rte_ticketlock.h        |  3 +-
 14 files changed, 163 insertions(+), 13 deletions(-)