From: Sirshak Das <sirshak.das@arm.com>
Date: Tue, 5 Feb 2019 07:33:33 +0000 (-0600)
Subject: svm_fifo rework to avoid contention on cursize
X-Git-Tag: v20.01-rc0~807
X-Git-Url: https://gerrit.fd.io/r/gitweb?a=commitdiff_plain;h=28aa539f7da7b172d0f35ea9a63f3986939477f7;hp=28aa539f7da7b172d0f35ea9a63f3986939477f7;p=vpp.git

svm_fifo rework to avoid contention on cursize

Problems Addressed:
- Contention of cursize by producer and consumer.
- Reduce the no of modulo operations.

Changes:
- Synchronization between producer and consumer changed from cursize
  to head and tail indexes
  Implications: reduces the usable size of fifo by 1.
- Using weaker memory ordering C++11 atomics to access head and tail
  based on producer and consumer role.
- Head and tail indexes are unsigned 32 bit integers. Additions and
  subtraction on them are implicit 32 bit Modulo operation.
- Adding weaker memory ordering variants of max_enq, max_deq, is_empty
  and is_full Using them appropriately in all places.

Perfomance improvement (iperf3 via Hoststack):

iperf3 Server: Marvell ThunderX2(AArch64) - iperf3 Client: Skylake(x86)
   ~6%(256 rxd/txd) - ~11%(2048 rxd/txd)

Change-Id: I1d484e000e437430fdd5a819657d1c6b62443018
Signed-off-by: Sirshak Das <sirshak.das@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
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