| Message ID | 20161206205627.8443-2-bobby.prani@gmail.com |
|---|---|
| State | New |
| Headers | show |
Pranith Kumar <bobby.prani@gmail.com> writes: > We acquire mmap lock and tb lock in one order and release them in a > different order. This does not need to be that way. > > This patch was inspired by a previous patch by Emilio G. Cota > (https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg03785.html). > > Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> > --- > cpu-exec.c | 12 +++--------- > 1 file changed, 3 insertions(+), 9 deletions(-) > > diff --git a/cpu-exec.c b/cpu-exec.c > index aa8318d864..f4a00f5047 100644 > --- a/cpu-exec.c > +++ b/cpu-exec.c > @@ -318,7 +318,6 @@ static inline TranslationBlock *tb_find(CPUState *cpu, > TranslationBlock *tb; > target_ulong cs_base, pc; > uint32_t flags; > - bool have_tb_lock = false; > > /* we record a subset of the CPU state. It will > always be the same before a given translated block > @@ -336,7 +335,6 @@ static inline TranslationBlock *tb_find(CPUState *cpu, > */ > mmap_lock(); > tb_lock(); > - have_tb_lock = true; > > /* There's a chance that our desired tb has been translated while > * taking the locks so we check again inside the lock. > @@ -347,6 +345,7 @@ static inline TranslationBlock *tb_find(CPUState *cpu, > tb = tb_gen_code(cpu, pc, cs_base, flags, 0); > } > > + tb_unlock(); > mmap_unlock(); > } > > @@ -364,17 +363,12 @@ 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 (!have_tb_lock) { > - tb_lock(); > - have_tb_lock = true; > - } > if (!tb->invalid) { > + tb_lock(); > tb_add_jump(last_tb, tb_exit, tb); > + tb_unlock(); > } > } > - if (have_tb_lock) { > - tb_unlock(); > - } > return tb; > } Do you have any numbers for this? The main reason being we are trying to avoid bouncing the lock too much and while this is cleaner it could cause more contention. -- Alex Bennée
diff --git a/cpu-exec.c b/cpu-exec.c index aa8318d864..f4a00f5047 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -318,7 +318,6 @@ static inline TranslationBlock *tb_find(CPUState *cpu, TranslationBlock *tb; target_ulong cs_base, pc; uint32_t flags; - bool have_tb_lock = false; /* we record a subset of the CPU state. It will always be the same before a given translated block @@ -336,7 +335,6 @@ static inline TranslationBlock *tb_find(CPUState *cpu, */ mmap_lock(); tb_lock(); - have_tb_lock = true; /* There's a chance that our desired tb has been translated while * taking the locks so we check again inside the lock. @@ -347,6 +345,7 @@ static inline TranslationBlock *tb_find(CPUState *cpu, tb = tb_gen_code(cpu, pc, cs_base, flags, 0); } + tb_unlock(); mmap_unlock(); } @@ -364,17 +363,12 @@ 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 (!have_tb_lock) { - tb_lock(); - have_tb_lock = true; - } if (!tb->invalid) { + tb_lock(); tb_add_jump(last_tb, tb_exit, tb); + tb_unlock(); } } - if (have_tb_lock) { - tb_unlock(); - } return tb; }
We acquire mmap lock and tb lock in one order and release them in a different order. This does not need to be that way. This patch was inspired by a previous patch by Emilio G. Cota (https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg03785.html). Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> --- cpu-exec.c | 12 +++--------- 1 file changed, 3 insertions(+), 9 deletions(-)