[Qemu-devel] [PATCH v2 0/9] tcg: signal-free qemu_cpu_kick

[Paolo Bonzini]

This version of the signal-free qemu_cpu_kick patches is, ehm, much
better.  Variable are accessed either with Java-style volatiles or
protected by memory barriers, and the cleanups go further by removing
qemu/tls.h and C volatiles.

The logic is relatively simple.  The I/O thread does (letters in
parentheses indicates the synchronizes-with edges):

    run_on_cpu or similar
    ...
    seq_cst write 1 to exit_request        (C)
    seq_cst read tcg_current_cpu to cpu    (B)
    if not NULL
       write 1 to cpu->exit_request
       release barrier                     (A)
       write 1 to cpu->tcg_exit_req

The CPU thread does either this:

    (in generated code) read cpu->tcg_exit_req
    acquire barrier                        (A)
    read cpu->exit_request
    exit from cpu_exec
    seq_cst write 0 to exit_request
    ...
    flush_queued_work or similar

or this:

    seq_cst write to tcg_current_cpu       (B)
    seq_cst read from exit_request         (C)
    exit from cpu_exec
    seq_cst write 0 to exit_request
    ...
    flush_queued_work or similar

The non-TLS tcg_current_cpu will go away with multi-threaded TCG.

Paolo

Paolo Bonzini (9):
  i8257: rewrite DMA_schedule to avoid hooking into the CPU loop
  i8257: remove cpu_request_exit irq
  tcg: introduce tcg_current_cpu
  remove qemu/tls.h
  tcg: assign cpu->current_tb in a simpler place
  tcg: synchronize cpu->exit_request and cpu->tcg_exit_req accesses
  tcg: synchronize exit_request and tcg_current_cpu accesses
  use qemu_cpu_kick instead of cpu_exit or qemu_cpu_kick_thread
  tcg: signal-free qemu_cpu_kick

 cpu-exec.c              | 33 ++++++++----------
 cpus.c                  | 91 ++++++++++++++-----------------------------------
 exec.c                  |  2 +-
 gdbstub.c               |  2 +-
 hw/block/fdc.c          |  2 +-
 hw/dma/i82374.c         |  5 +--
 hw/dma/i8257.c          | 31 +++++++++--------
 hw/i386/pc.c            | 13 +------
 hw/isa/i82378.c         |  3 +-
 hw/mips/mips_fulong2e.c | 13 +------
 hw/mips/mips_jazz.c     | 13 +------
 hw/mips/mips_malta.c    | 13 +------
 hw/ppc/prep.c           | 11 ------
 hw/ppc/spapr_rtas.c     |  2 +-
 hw/sparc/sun4m.c        |  4 +--
 hw/sparc64/sun4u.c      |  4 +--
 include/exec/exec-all.h |  5 +--
 include/hw/isa/isa.h    |  4 +--
 include/qemu/tls.h      | 52 ----------------------------
 include/qom/cpu.h       |  8 ++---
 qom/cpu.c               |  2 ++
 21 files changed, 80 insertions(+), 233 deletions(-)
 delete mode 100644 include/qemu/tls.h

-- 
2.4.3