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tcg: remove tb_lock

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Use mmap_lock in user-mode to protect TCG state and the page descriptors.
In !user-mode, each vCPU has its own TCG state, so no locks needed.
Per-page locks are used to protect the page descriptors.

Per-TB locks are used in both modes to protect TB jumps.

Some notes:

- tb_lock is removed from notdirty_mem_write by passing a
  locked page_collection to tb_invalidate_phys_page_fast.

- tcg_tb_lookup/remove/insert/etc have their own internal lock(s),
  so there is no need to further serialize access to them.

- do_tb_flush is run in a safe async context, meaning no other
  vCPU threads are running. Therefore acquiring mmap_lock there
  is just to please tools such as thread sanitizer.

- Not visible in the diff, but tb_invalidate_phys_page already
  has an assert_memory_lock.

- cpu_io_recompile is !user-only, so no mmap_lock there.

- Added mmap_unlock()'s before all siglongjmp's that could
  be called in user-mode while mmap_lock is held.
  + Added an assert for !have_mmap_lock() after returning from
    the longjmp in cpu_exec, just like we do in cpu_exec_step_atomic.

Performance numbers before/after:

Host: AMD Opteron(tm) Processor 6376

                 ubuntu 17.04 ppc64 bootup+shutdown time

  700 +-+--+----+------+------------+-----------+------------*--+-+
      |    +    +      +            +           +           *B    |
      |         before ***B***                            ** *    |
      |tb lock removal ###D###                         ***        |
  600 +-+                                           ***         +-+
      |                                           **         #    |
      |                                        *B*          #D    |
      |                                     *** *         ##      |
  500 +-+                                ***           ###      +-+
      |                             * ***           ###           |
      |                            *B*          # ##              |
      |                          ** *          #D#                |
  400 +-+                      **            ##                 +-+
      |                      **           ###                     |
      |                    **           ##                        |
      |                  **         # ##                          |
  300 +-+  *           B*          #D#                          +-+
      |    B         ***        ###                               |
      |    *       **       ####                                  |
      |     *   ***      ###                                      |
  200 +-+   B  *B     #D#                                       +-+
      |     #B* *   ## #                                          |
      |     #*    ##                                              |
      |    + D##D#     +            +           +            +    |
  100 +-+--+----+------+------------+-----------+------------+--+-+
           1    8      16      Guest CPUs       48           64
  png: https://imgur.com/HwmBHXe

              debian jessie aarch64 bootup+shutdown time

  90 +-+--+-----+-----+------------+------------+------------+--+-+
     |    +     +     +            +            +            +    |
     |         before ***B***                                B    |
  80 +tb lock removal ###D###                              **D  +-+
     |                                                   **###    |
     |                                                 **##       |
  70 +-+                                             ** #       +-+
     |                                             ** ##          |
     |                                           **  #            |
  60 +-+                                       *B  ##           +-+
     |                                       **  ##               |
     |                                    ***  #D                 |
  50 +-+                               ***   ##                 +-+
     |                             * **   ###                     |
     |                           **B*  ###                        |
  40 +-+                     ****  # ##                         +-+
     |                   ****     #D#                             |
     |             ***B**      ###                                |
  30 +-+    B***B**        ####                                 +-+
     |    B *   *     # ###                                       |
     |     B       ###D#                                          |
  20 +-+   D  ##D##                                             +-+
     |      D#                                                    |
     |    +     +     +            +            +            +    |
  10 +-+--+-----+-----+------------+------------+------------+--+-+
          1     8     16      Guest CPUs        48           64
  png: https://imgur.com/iGpGFtv

The gains are high for 4-8 CPUs. Beyond that point, however, unrelated
lock contention significantly hurts scalability.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Emilio G. Cota 2017-08-04 23:46:31 -04:00 • committed by Richard Henderson
parent 705ad1ff0c
commit 0ac20318ce
11 changed files with 75 additions and 152 deletions
Download patch file Download diff file Expand all files Collapse all files

26
exec.c
View file

@ -1031,9 +1031,7 @@ const char *parse_cpu_model(const char *cpu_model)
static void breakpoint_invalidate(CPUState *cpu, target_ulong pc)
{
mmap_lock();
tb_lock();
tb_invalidate_phys_page_range(pc, pc + 1, 0);
tb_unlock();
mmap_unlock();
}
#else
@ -2644,21 +2642,21 @@ void memory_notdirty_write_prepare(NotDirtyInfo *ndi,
ndi->ram_addr = ram_addr;
ndi->mem_vaddr = mem_vaddr;
ndi->size = size;
ndi->locked = false;
ndi->pages = NULL;
assert(tcg_enabled());
if (!cpu_physical_memory_get_dirty_flag(ram_addr, DIRTY_MEMORY_CODE)) {
ndi->locked = true;
tb_lock();
tb_invalidate_phys_page_fast(ram_addr, size);
ndi->pages = page_collection_lock(ram_addr, ram_addr + size);
tb_invalidate_phys_page_fast(ndi->pages, ram_addr, size);
}
}
/* Called within RCU critical section. */
void memory_notdirty_write_complete(NotDirtyInfo *ndi)
{
if (ndi->locked) {
tb_unlock();
if (ndi->pages) {
page_collection_unlock(ndi->pages);
ndi->pages = NULL;
}
/* Set both VGA and migration bits for simplicity and to remove
@ -2745,18 +2743,16 @@ static void check_watchpoint(int offset, int len, MemTxAttrs attrs, int flags)
}
cpu->watchpoint_hit = wp;
/* Both tb_lock and iothread_mutex will be reset when
* cpu_loop_exit or cpu_loop_exit_noexc longjmp
* back into the cpu_exec main loop.
*/
tb_lock();
mmap_lock();
tb_check_watchpoint(cpu);
if (wp->flags & BP_STOP_BEFORE_ACCESS) {
cpu->exception_index = EXCP_DEBUG;
mmap_unlock();
cpu_loop_exit(cpu);
} else {
/* Force execution of one insn next time. */
cpu->cflags_next_tb = 1 | curr_cflags();
mmap_unlock();
cpu_loop_exit_noexc(cpu);
}
}
@ -3147,9 +3143,9 @@ static void invalidate_and_set_dirty(MemoryRegion *mr, hwaddr addr,
}
if (dirty_log_mask & (1 << DIRTY_MEMORY_CODE)) {
assert(tcg_enabled());
tb_lock();
mmap_lock();
tb_invalidate_phys_range(addr, addr + length);
tb_unlock();
mmap_unlock();
dirty_log_mask &= ~(1 << DIRTY_MEMORY_CODE);
}
cpu_physical_memory_set_dirty_range(addr, length, dirty_log_mask);