| Message ID | 1467735496-16256-7-git-send-email-alex.bennee@linaro.org |
|---|---|
| State | New |
| Headers | show |
Sergey Fedorov <sergey.fedorov@linaro.org> writes: > From: Sergey Fedorov <serge.fdrv@gmail.com> > > Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com> > Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org> > --- > 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. > } > > /* 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
Sergey Fedorov <serge.fdrv@gmail.com> writes: > On 07/07/16 22:46, Sergey Fedorov wrote: >> On 07/07/16 22:36, Alex Bennée wrote: >>> Sergey Fedorov <sergey.fedorov@linaro.org> writes: >>> >>>> From: Sergey Fedorov <serge.fdrv@gmail.com> >>>> >>>> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com> >>>> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org> >>>> --- >>>> 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 */ >> >> > > Using goto statements, the lines from tb_find_slow() which take the > locks can even be on the same indentation level as the lines resetting > them. I could prepare a patch series based on your first 3 patches and > this idea. Sure, lets see what it looks like ;-) > > 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 -- Alex Bennée
diff --git a/cpu-exec.c b/cpu-exec.c index 59c2ec5..529eae1 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -281,7 +281,8 @@ static TranslationBlock *tb_find_physical(CPUState *cpu, /* * Patch the last TB with a jump to the current TB. * - * Modification of the TB has to be protected with tb_lock. + * Modification of the TB has to be protected with tb_lock which can + * either be already held or taken here. */ static inline void maybe_patch_last_tb(CPUState *cpu, TranslationBlock *tb, @@ -306,72 +307,86 @@ static inline void maybe_patch_last_tb(CPUState *cpu, #endif /* See if we can patch the calling TB. */ if (*last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) { - tb_lock(); + bool locked = tb_lock_recursive(); tb_add_jump(*last_tb, tb_exit, tb); - tb_unlock(); - } -} - -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. - */ - 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); + if (locked) { + tb_unlock(); } - - tb_unlock(); - 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); - return tb; } -static inline TranslationBlock *tb_find_fast(CPUState *cpu, - TranslationBlock **last_tb, - int tb_exit) +/* + * tb_find - find next TB, possibly generating it + * + * There is a multi-level lookup for finding the next TB which avoids + * locks unless generation is required. + * + * 1. Lookup via the per-vcpu tb_jmp_cache + * 2. Lookup via tb_find_physical (using QHT) + * + * If both of those fail then we need to grab the mmap_lock and + * tb_lock and do code generation. + * + * As the jump patching of code also needs to be protected by locks we + * have multiple paths into maybe_patch_last_tb taking advantage of + * the fact we may already have locks held for code generation. + */ +static TranslationBlock *tb_find(CPUState *cpu, + TranslationBlock **last_tb, + int tb_exit) { CPUArchState *env = (CPUArchState *)cpu->env_ptr; TranslationBlock *tb; target_ulong cs_base, pc; + unsigned int h; uint32_t flags; /* we record a subset of the CPU state. It will always be the same before a given translated block is executed. */ cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags); - tb = atomic_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]); + h = tb_jmp_cache_hash_func(pc); + tb = atomic_read(&cpu->tb_jmp_cache[h]); + if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base || tb->flags != flags)) { - tb = tb_find_slow(cpu, pc, cs_base, flags); - } - maybe_patch_last_tb(cpu, tb, last_tb, tb_exit); + /* 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. + */ + 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); + } + maybe_patch_last_tb(cpu, tb, last_tb, tb_exit); + + tb_unlock(); + mmap_unlock(); + } else { + maybe_patch_last_tb(cpu, tb, last_tb, tb_exit); + } + + /* We update the TB in the virtual pc hash table for the fast lookup */ + atomic_set(&cpu->tb_jmp_cache[h], tb); + } else { + maybe_patch_last_tb(cpu, tb, last_tb, tb_exit); + } return tb; } @@ -452,7 +467,7 @@ 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 @@ -636,7 +651,7 @@ 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 */
In an effort not to re-take locks I've re-factored the code so everything is done inside the new tb_find function. The fast path will only take a lock if the previous TB needs patching. The generation path will do the patching inside the generation critical section. Signed-off-by: Alex Bennée <alex.bennee@linaro.org> --- cpu-exec.c | 117 ++++++++++++++++++++++++++++++++++--------------------------- 1 file changed, 66 insertions(+), 51 deletions(-) -- 2.7.4