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Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_
From: |
Sergey Fedorov |
Subject: |
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump() |
Date: |
Thu, 7 Jul 2016 22:46:34 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 |
On 07/07/16 22:36, Alex Bennée wrote:
> Sergey Fedorov <address@hidden> writes:
>
>> From: Sergey Fedorov <address@hidden>
>>
>> Signed-off-by: Sergey Fedorov <address@hidden>
>> Signed-off-by: Sergey Fedorov <address@hidden>
>> ---
>> cpu-exec.c | 15 +++++++++------
>> 1 file changed, 9 insertions(+), 6 deletions(-)
>>
>> diff --git a/cpu-exec.c b/cpu-exec.c
>> index dd0bd5007701..54c935039592 100644
>> --- a/cpu-exec.c
>> +++ b/cpu-exec.c
>> @@ -295,7 +295,8 @@ static TranslationBlock *tb_find_slow(CPUState *cpu,
>>
>> /* 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.
>> + * single threaded the locks are NOPs. Both locks are to be
>> + * released at the end of tb_find_fast().
>> */
>> mmap_lock();
>> tb_lock();
>> @@ -308,9 +309,6 @@ static TranslationBlock *tb_find_slow(CPUState *cpu,
>> /* if no translated code available, then translate it now */
>> tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
>> }
>> -
>> - tb_unlock();
>> - mmap_unlock();
> Hmm pushing these outside of tb_find_slow() makes me uncomfortable. I
> guess tb_find_fast/slow are intimately tied together but the idea of
> taking locks which are the responsibility of the calling function to
> clear seems ugly to me.
Okay, what if we also:
diff --git a/cpu-exec.c b/cpu-exec.c
index 54c935039592..ff8f92bc1dc1 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -278,45 +278,7 @@ static TranslationBlock *tb_find_physical(CPUState
*cpu,
return qht_lookup(&tcg_ctx.tb_ctx.htable, tb_cmp, &desc, h);
}
-static TranslationBlock *tb_find_slow(CPUState *cpu,
- target_ulong pc,
- target_ulong cs_base,
- uint32_t flags)
-{
- TranslationBlock *tb;
-
- /* Ensure that we won't find a TB in the shared hash table
- * if it is being invalidated by some other thread.
- * Otherwise we'd put it back to CPU's local cache.
- * Pairs with smp_wmb() in tb_phys_invalidate(). */
- smp_rmb();
- tb = tb_find_physical(cpu, pc, cs_base, flags);
- if (!tb) {
-
- /* 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. Both locks are to be
- * released at the end of tb_find_fast().
- */
- mmap_lock();
- tb_lock();
-
- /* There's a chance that our desired tb has been translated while
- * taking the locks so we check again inside the lock.
- */
- tb = tb_find_physical(cpu, pc, cs_base, flags);
- if (!tb) {
- /* if no translated code available, then translate it now */
- tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
- }
- }
-
- /* 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);
- return tb;
-}
-
-static inline TranslationBlock *tb_find_fast(CPUState *cpu,
+static inline TranslationBlock *tb_find(CPUState *cpu,
TranslationBlock **last_tb,
int tb_exit)
{
@@ -332,7 +294,34 @@ static inline TranslationBlock
*tb_find_fast(CPUState *cpu,
tb = atomic_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
tb->flags != flags)) {
- tb = tb_find_slow(cpu, pc, cs_base, flags);
+ /* Ensure that we won't find a TB in the shared hash table
+ * if it is being invalidated by some other thread.
+ * Otherwise we'd put it back to CPU's local cache.
+ * Pairs with smp_wmb() in tb_phys_invalidate(). */
+ smp_rmb();
+ tb = tb_find_physical(cpu, pc, cs_base, flags);
+ if (!tb) {
+
+ /* 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. Both locks are to be
+ * released at the end of the function.
+ */
+ mmap_lock();
+ tb_lock();
+
+ /* There's a chance that our desired tb has been translated
while
+ * taking the locks so we check again inside the lock.
+ */
+ tb = tb_find_physical(cpu, pc, cs_base, flags);
+ if (!tb) {
+ /* if no translated code available, then translate it
now */
+ tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
+ }
+ }
+
+ /* 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);
}
if (cpu->tb_flushed) {
/* Ensure that no TB jump will be modified as the
@@ -440,7 +429,7 @@ static inline bool cpu_handle_exception(CPUState
*cpu, int *ret)
&& cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
/* try to cause an exception pending in the log */
TranslationBlock *last_tb = NULL; /* Avoid chaining TBs */
- cpu_exec_nocache(cpu, 1, tb_find_fast(cpu, &last_tb, 0), true);
+ cpu_exec_nocache(cpu, 1, tb_find(cpu, &last_tb, 0), true);
*ret = -1;
return true;
#endif
@@ -624,7 +613,7 @@ int cpu_exec(CPUState *cpu)
cpu->tb_flushed = false; /* reset before first TB lookup */
for(;;) {
cpu_handle_interrupt(cpu, &last_tb);
- tb = tb_find_fast(cpu, &last_tb, tb_exit);
+ tb = tb_find(cpu, &last_tb, tb_exit);
cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
/* Try to align the host and virtual clocks
if the guest is in advance */
Kind regards,
Sergey
>
>> }
>>
>> /* We add the TB in the virtual pc hash table for the fast lookup */
>> @@ -354,10 +352,15 @@ static inline TranslationBlock *tb_find_fast(CPUState
>> *cpu,
>> #endif
>> /* See if we can patch the calling TB. */
>> if (*last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
>> - tb_lock();
>> + if (!tb_lock_locked()) {
>> + tb_lock();
>> + }
>> tb_add_jump(*last_tb, tb_exit, tb);
>> - tb_unlock();
>> }
>> +
>> + tb_lock_reset();
>> + mmap_lock_reset();
>> +
>> return tb;
>> }
>
> --
> Alex Bennée
- Re: [Qemu-devel] [PATCH v2 3/6] tcg: cpu-exec: remove tb_lock from the hot-path, (continued)
Re: [Qemu-devel] [PATCH v2 3/6] tcg: cpu-exec: remove tb_lock from the hot-path, Sergey Fedorov, 2016/07/08
[Qemu-devel] [PATCH v2 6/6] tcg: cpu-exec: roll-up tb_find_fast/slow, Alex Bennée, 2016/07/05
- Re: [Qemu-devel] [PATCH v2 6/6] tcg: cpu-exec: roll-up tb_find_fast/slow, Sergey Fedorov, 2016/07/07
- [Qemu-devel] [PATCH 2/3] tcg: Introduce tb_lock_locked(), Sergey Fedorov, 2016/07/07
- [Qemu-devel] [PATCH 1/3] tcg: Introduce mmap_lock_reset(), Sergey Fedorov, 2016/07/07
- [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/07
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Alex Bennée, 2016/07/07
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(),
Sergey Fedorov <=
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/07
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Alex Bennée, 2016/07/07
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/08
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/08
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/08
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/08
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/08
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/08
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/08
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/08