mirror of
https://github.com/Motorhead1991/qemu.git
synced 2025-08-04 16:23:55 -06:00
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>
This commit is contained in:
Emilio G. Cota
Richard Henderson
parent
705ad1ff0c
commit
0ac20318ce
11 changed files with 75 additions and 152 deletions
|
|
@ -212,20 +212,20 @@ static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
|
|||
We only end up here when an existing TB is too long. */
|
||||
cflags |= MIN(max_cycles, CF_COUNT_MASK);
|
||||
|
||||
tb_lock();
|
||||
mmap_lock();
|
||||
tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base,
|
||||
orig_tb->flags, cflags);
|
||||
tb->orig_tb = orig_tb;
|
||||
tb_unlock();
|
||||
mmap_unlock();
|
||||
|
||||
/* execute the generated code */
|
||||
trace_exec_tb_nocache(tb, tb->pc);
|
||||
cpu_tb_exec(cpu, tb);
|
||||
|
||||
tb_lock();
|
||||
mmap_lock();
|
||||
tb_phys_invalidate(tb, -1);
|
||||
mmap_unlock();
|
||||
tcg_tb_remove(tb);
|
||||
tb_unlock();
|
||||
}
|
||||
#endif
|
||||
|
||||
|
|
@ -244,9 +244,7 @@ void cpu_exec_step_atomic(CPUState *cpu)
|
|||
tb = tb_lookup__cpu_state(cpu, &pc, &cs_base, &flags, cf_mask);
|
||||
if (tb == NULL) {
|
||||
mmap_lock();
|
||||
tb_lock();
|
||||
tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
|
||||
tb_unlock();
|
||||
mmap_unlock();
|
||||
}
|
||||
|
||||
|
|
@ -261,15 +259,13 @@ void cpu_exec_step_atomic(CPUState *cpu)
|
|||
cpu_tb_exec(cpu, tb);
|
||||
cc->cpu_exec_exit(cpu);
|
||||
} else {
|
||||
/* We may have exited due to another problem here, so we need
|
||||
* to reset any tb_locks we may have taken but didn't release.
|
||||
/*
|
||||
* The mmap_lock is dropped by tb_gen_code if it runs out of
|
||||
* memory.
|
||||
*/
|
||||
#ifndef CONFIG_SOFTMMU
|
||||
tcg_debug_assert(!have_mmap_lock());
|
||||
#endif
|
||||
tb_lock_reset();
|
||||
assert_no_pages_locked();
|
||||
}
|
||||
|
||||
|
|
@ -398,20 +394,11 @@ static inline TranslationBlock *tb_find(CPUState *cpu,
|
|||
TranslationBlock *tb;
|
||||
target_ulong cs_base, pc;
|
||||
uint32_t flags;
|
||||
bool acquired_tb_lock = false;
|
||||
|
||||
tb = tb_lookup__cpu_state(cpu, &pc, &cs_base, &flags, cf_mask);
|
||||
if (tb == NULL) {
|
||||
/* mmap_lock is needed by tb_gen_code, and mmap_lock must be
|
||||
* taken outside tb_lock. As system emulation is currently
|
||||
* single threaded the locks are NOPs.
|
||||
*/
|
||||
mmap_lock();
|
||||
tb_lock();
|
||||
acquired_tb_lock = true;
|
||||
|
||||
tb = tb_gen_code(cpu, pc, cs_base, flags, cf_mask);
|
||||
|
||||
mmap_unlock();
|
||||
/* We add the TB in the virtual pc hash table for the fast lookup */
|
||||
atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
|
||||
|
|
@ -427,15 +414,8 @@ static inline TranslationBlock *tb_find(CPUState *cpu,
|
|||
#endif
|
||||
/* See if we can patch the calling TB. */
|
||||
if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
|
||||
if (!acquired_tb_lock) {
|
||||
tb_lock();
|
||||
acquired_tb_lock = true;
|
||||
}
|
||||
tb_add_jump(last_tb, tb_exit, tb);
|
||||
}
|
||||
if (acquired_tb_lock) {
|
||||
tb_unlock();
|
||||
}
|
||||
return tb;
|
||||
}
|
||||
|
||||
|
|
@ -710,7 +690,9 @@ int cpu_exec(CPUState *cpu)
|
|||
g_assert(cpu == current_cpu);
|
||||
g_assert(cc == CPU_GET_CLASS(cpu));
|
||||
#endif /* buggy compiler */
|
||||
tb_lock_reset();
|
||||
#ifndef CONFIG_SOFTMMU
|
||||
tcg_debug_assert(!have_mmap_lock());
|
||||
#endif
|
||||
if (qemu_mutex_iothread_locked()) {
|
||||
qemu_mutex_unlock_iothread();
|
||||
}
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue