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author | Emilio G. Cota <cota@braap.org> | 2017-08-04 23:46:31 -0400 |
---|---|---|
committer | Richard Henderson <richard.henderson@linaro.org> | 2018-06-15 08:18:48 -1000 |
commit | 0ac20318ce16f4de288969b2007ef5a654176058 (patch) | |
tree | ba285e1540b4d875b476acd72f364d8aaa7165d5 /exec.c | |
parent | 705ad1ff0ce264475cb4c9a3aa31ba94a04869fe (diff) | |
download | qemu-0ac20318ce16f4de288969b2007ef5a654176058.zip qemu-0ac20318ce16f4de288969b2007ef5a654176058.tar.gz qemu-0ac20318ce16f4de288969b2007ef5a654176058.tar.bz2 |
tcg: remove tb_lock
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>
Diffstat (limited to 'exec.c')
-rw-r--r-- | exec.c | 26 |
1 files changed, 11 insertions, 15 deletions
@@ -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); |