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tcg: track TBs with per-region BST's

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This paves the way for enabling scalable parallel generation of TCG code.

Instead of tracking TBs with a single binary search tree (BST), use a
BST for each TCG region, protecting it with a lock. This is as scalable
as it gets, since each TCG thread operates on a separate region.

The core of this change is the introduction of struct tcg_region_tree,
which contains a pointer to a GTree and an associated lock to serialize
accesses to it. We then allocate an array of tcg_region_tree's, adding
the appropriate padding to avoid false sharing based on
qemu_dcache_linesize.

Given a tc_ptr, we first find the corresponding region_tree. This
is done by special-casing the first and last regions first, since they
might be of size != region.size; otherwise we just divide the offset
by region.stride. I was worried about this division (several dozen
cycles of latency), but profiling shows that this is not a fast path.
Note that region.stride is not required to be a power of two; it
is only required to be a multiple of the host's page size.

Note that with this design we can also provide consistent snapshots
about all region trees at once; for instance, tcg_tb_foreach
acquires/releases all region_tree locks before/after iterating over them.
For this reason we now drop tb_lock in dump_exec_info().

As an alternative I considered implementing a concurrent BST, but this
can be tricky to get right, offers no consistent snapshots of the BST,
and performance and scalability-wise I don't think it could ever beat
having separate GTrees, given that our workload is insert-mostly (all
concurrent BST designs I've seen focus, understandably, on making
lookups fast, which comes at the expense of convoluted, non-wait-free
insertions/removals).

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 2017-07-26 16:58:05 -04:00 committed by Richard Henderson
parent 32359d529f
commit be2cdc5e35
6 changed files with 213 additions and 89 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
accel/tcg/cpu-exec.c
View File

@ -224,7 +224,7 @@ static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
tb_lock();
tb_phys_invalidate(tb, -1);
tb_remove(tb);
tcg_tb_remove(tb);
tb_unlock();
}
#endif

101
accel/tcg/translate-all.c
View File

@ -205,8 +205,6 @@ void tb_lock_reset(void)
}
}
static TranslationBlock *tb_find_pc(uintptr_t tc_ptr);
void cpu_gen_init(void)
{
tcg_context_init(&tcg_init_ctx);
@ -375,13 +373,13 @@ bool cpu_restore_state(CPUState *cpu, uintptr_t host_pc, bool will_exit)
if (check_offset < tcg_init_ctx.code_gen_buffer_size) {
tb_lock();
tb = tb_find_pc(host_pc);
tb = tcg_tb_lookup(host_pc);
if (tb) {
cpu_restore_state_from_tb(cpu, tb, host_pc, will_exit);
if (tb->cflags & CF_NOCACHE) {
/* one-shot translation, invalidate it immediately */
tb_phys_invalidate(tb, -1);
tb_remove(tb);
tcg_tb_remove(tb);
}
r = true;
}
@ -728,48 +726,6 @@ static inline void *alloc_code_gen_buffer(void)
}
#endif /* USE_STATIC_CODE_GEN_BUFFER, WIN32, POSIX */
/* compare a pointer @ptr and a tb_tc @s */
static int ptr_cmp_tb_tc(const void *ptr, const struct tb_tc *s)
{
if (ptr >= s->ptr + s->size) {
return 1;
} else if (ptr < s->ptr) {
return -1;
}
return 0;
}
static gint tb_tc_cmp(gconstpointer ap, gconstpointer bp)
{
const struct tb_tc *a = ap;
const struct tb_tc *b = bp;
/*
* When both sizes are set, we know this isn't a lookup.
* This is the most likely case: every TB must be inserted; lookups
* are a lot less frequent.
*/
if (likely(a->size && b->size)) {
if (a->ptr > b->ptr) {
return 1;
} else if (a->ptr < b->ptr) {
return -1;
}
/* a->ptr == b->ptr should happen only on deletions */
g_assert(a->size == b->size);
return 0;
}
/*
* All lookups have either .size field set to 0.
* From the glib sources we see that @ap is always the lookup key. However
* the docs provide no guarantee, so we just mark this case as likely.
*/
if (likely(a->size == 0)) {
return ptr_cmp_tb_tc(a->ptr, b);
}
return ptr_cmp_tb_tc(b->ptr, a);
}
static inline void code_gen_alloc(size_t tb_size)
{
tcg_ctx->code_gen_buffer_size = size_code_gen_buffer(tb_size);
@ -778,7 +734,6 @@ static inline void code_gen_alloc(size_t tb_size)
fprintf(stderr, "Could not allocate dynamic translator buffer\n");
exit(1);
}
tb_ctx.tb_tree = g_tree_new(tb_tc_cmp);
qemu_mutex_init(&tb_ctx.tb_lock);
}
@ -839,14 +794,6 @@ static TranslationBlock *tb_alloc(target_ulong pc)
return tb;
}
/* Called with tb_lock held. */
void tb_remove(TranslationBlock *tb)
{
assert_tb_locked();
g_tree_remove(tb_ctx.tb_tree, &tb->tc);
}
static inline void invalidate_page_bitmap(PageDesc *p)
{
#ifdef CONFIG_SOFTMMU
@ -911,10 +858,10 @@ static void do_tb_flush(CPUState *cpu, run_on_cpu_data tb_flush_count)
}
if (DEBUG_TB_FLUSH_GATE) {
size_t nb_tbs = g_tree_nnodes(tb_ctx.tb_tree);
size_t nb_tbs = tcg_nb_tbs();
size_t host_size = 0;
g_tree_foreach(tb_ctx.tb_tree, tb_host_size_iter, &host_size);
tcg_tb_foreach(tb_host_size_iter, &host_size);
printf("qemu: flush code_size=%zu nb_tbs=%zu avg_tb_size=%zu\n",
tcg_code_size(), nb_tbs, nb_tbs > 0 ? host_size / nb_tbs : 0);
}
@ -923,10 +870,6 @@ static void do_tb_flush(CPUState *cpu, run_on_cpu_data tb_flush_count)
cpu_tb_jmp_cache_clear(cpu);
}
/* Increment the refcount first so that destroy acts as a reset */
g_tree_ref(tb_ctx.tb_tree);
g_tree_destroy(tb_ctx.tb_tree);
qht_reset_size(&tb_ctx.htable, CODE_GEN_HTABLE_SIZE);
page_flush_tb();
@ -1406,7 +1349,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
* through the physical hash table and physical page list.
*/
tb_link_page(tb, phys_pc, phys_page2);
g_tree_insert(tb_ctx.tb_tree, &tb->tc, tb);
tcg_tb_insert(tb);
return tb;
}
@ -1510,7 +1453,7 @@ void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end,
current_tb = NULL;
if (cpu->mem_io_pc) {
/* now we have a real cpu fault */
current_tb = tb_find_pc(cpu->mem_io_pc);
current_tb = tcg_tb_lookup(cpu->mem_io_pc);
}
}
if (current_tb == tb &&
@ -1627,7 +1570,7 @@ static bool tb_invalidate_phys_page(tb_page_addr_t addr, uintptr_t pc)
tb = p->first_tb;
#ifdef TARGET_HAS_PRECISE_SMC
if (tb && pc != 0) {
current_tb = tb_find_pc(pc);
current_tb = tcg_tb_lookup(pc);
}
if (cpu != NULL) {
env = cpu->env_ptr;
@ -1670,18 +1613,6 @@ static bool tb_invalidate_phys_page(tb_page_addr_t addr, uintptr_t pc)
}
#endif
/*
* Find the TB 'tb' such that
* tb->tc.ptr <= tc_ptr < tb->tc.ptr + tb->tc.size
* Return NULL if not found.
*/
static TranslationBlock *tb_find_pc(uintptr_t tc_ptr)
{
struct tb_tc s = { .ptr = (void *)tc_ptr };
return g_tree_lookup(tb_ctx.tb_tree, &s);
}
#if !defined(CONFIG_USER_ONLY)
void tb_invalidate_phys_addr(AddressSpace *as, hwaddr addr, MemTxAttrs attrs)
{
@ -1709,7 +1640,7 @@ void tb_check_watchpoint(CPUState *cpu)
{
TranslationBlock *tb;
tb = tb_find_pc(cpu->mem_io_pc);
tb = tcg_tb_lookup(cpu->mem_io_pc);
if (tb) {
/* We can use retranslation to find the PC. */
cpu_restore_state_from_tb(cpu, tb, cpu->mem_io_pc, true);
@ -1743,7 +1674,7 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr)
uint32_t n;
tb_lock();
tb = tb_find_pc(retaddr);
tb = tcg_tb_lookup(retaddr);
if (!tb) {
cpu_abort(cpu, "cpu_io_recompile: could not find TB for pc=%p",
(void *)retaddr);
@ -1782,7 +1713,7 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr)
* cpu_exec_nocache() */
tb_phys_invalidate(tb->orig_tb, -1);
}
tb_remove(tb);
tcg_tb_remove(tb);
}
/* TODO: If env->pc != tb->pc (i.e. the faulting instruction was not
@ -1853,6 +1784,7 @@ static void print_qht_statistics(FILE *f, fprintf_function cpu_fprintf,
}
struct tb_tree_stats {
size_t nb_tbs;
size_t host_size;
size_t target_size;
size_t max_target_size;
@ -1866,6 +1798,7 @@ static gboolean tb_tree_stats_iter(gpointer key, gpointer value, gpointer data)
const TranslationBlock *tb = value;
struct tb_tree_stats *tst = data;
tst->nb_tbs++;
tst->host_size += tb->tc.size;
tst->target_size += tb->size;
if (tb->size > tst->max_target_size) {
@ -1889,10 +1822,8 @@ void dump_exec_info(FILE *f, fprintf_function cpu_fprintf)
struct qht_stats hst;
size_t nb_tbs;
tb_lock();
nb_tbs = g_tree_nnodes(tb_ctx.tb_tree);
g_tree_foreach(tb_ctx.tb_tree, tb_tree_stats_iter, &tst);
tcg_tb_foreach(tb_tree_stats_iter, &tst);
nb_tbs = tst.nb_tbs;
/* XXX: avoid using doubles ? */
cpu_fprintf(f, "Translation buffer state:\n");
/*
@ -1927,8 +1858,6 @@ void dump_exec_info(FILE *f, fprintf_function cpu_fprintf)
cpu_fprintf(f, "TB invalidate count %d\n", tb_ctx.tb_phys_invalidate_count);
cpu_fprintf(f, "TLB flush count %zu\n", tlb_flush_count());
tcg_dump_info(f, cpu_fprintf);
tb_unlock();
}
void dump_opcount_info(FILE *f, fprintf_function cpu_fprintf)
@ -2196,7 +2125,7 @@ int page_unprotect(target_ulong address, uintptr_t pc)
* set the page to PAGE_WRITE and did the TB invalidate for us.
*/
#ifdef TARGET_HAS_PRECISE_SMC
TranslationBlock *current_tb = tb_find_pc(pc);
TranslationBlock *current_tb = tcg_tb_lookup(pc);
if (current_tb) {
current_tb_invalidated = tb_cflags(current_tb) & CF_INVALID;
}

1
include/exec/exec-all.h
View File

@ -405,7 +405,6 @@ static inline uint32_t curr_cflags(void)
| (use_icount ? CF_USE_ICOUNT : 0);
}
void tb_remove(TranslationBlock *tb);
void tb_flush(CPUState *cpu);
void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr);
TranslationBlock *tb_htable_lookup(CPUState *cpu, target_ulong pc,

1
include/exec/tb-context.h
View File

@ -31,7 +31,6 @@ typedef struct TBContext TBContext;
struct TBContext {
GTree *tb_tree;
struct qht htable;
/* any access to the tbs or the page table must use this lock */
QemuMutex tb_lock;

191
tcg/tcg.c
View File

@ -135,6 +135,12 @@ static TCGContext **tcg_ctxs;
static unsigned int n_tcg_ctxs;
TCGv_env cpu_env = 0;
struct tcg_region_tree {
QemuMutex lock;
GTree *tree;
/* padding to avoid false sharing is computed at run-time */
};
/*
* We divide code_gen_buffer into equally-sized "regions" that TCG threads
* dynamically allocate from as demand dictates. Given appropriate region
@ -158,6 +164,13 @@ struct tcg_region_state {
};
static struct tcg_region_state region;
/*
* This is an array of struct tcg_region_tree's, with padding.
* We use void * to simplify the computation of region_trees[i]; each
* struct is found every tree_size bytes.
*/
static void *region_trees;
static size_t tree_size;
static TCGRegSet tcg_target_available_regs[TCG_TYPE_COUNT];
static TCGRegSet tcg_target_call_clobber_regs;
@ -295,6 +308,180 @@ TCGLabel *gen_new_label(void)
#include "tcg-target.inc.c"
/* compare a pointer @ptr and a tb_tc @s */
static int ptr_cmp_tb_tc(const void *ptr, const struct tb_tc *s)
{
if (ptr >= s->ptr + s->size) {
return 1;
} else if (ptr < s->ptr) {
return -1;
}
return 0;
}
static gint tb_tc_cmp(gconstpointer ap, gconstpointer bp)
{
const struct tb_tc *a = ap;
const struct tb_tc *b = bp;
/*
* When both sizes are set, we know this isn't a lookup.
* This is the most likely case: every TB must be inserted; lookups
* are a lot less frequent.
*/
if (likely(a->size && b->size)) {
if (a->ptr > b->ptr) {
return 1;
} else if (a->ptr < b->ptr) {
return -1;
}
/* a->ptr == b->ptr should happen only on deletions */
g_assert(a->size == b->size);
return 0;
}
/*
* All lookups have either .size field set to 0.
* From the glib sources we see that @ap is always the lookup key. However
* the docs provide no guarantee, so we just mark this case as likely.
*/
if (likely(a->size == 0)) {
return ptr_cmp_tb_tc(a->ptr, b);
}
return ptr_cmp_tb_tc(b->ptr, a);
}
static void tcg_region_trees_init(void)
{
size_t i;
tree_size = ROUND_UP(sizeof(struct tcg_region_tree), qemu_dcache_linesize);
region_trees = qemu_memalign(qemu_dcache_linesize, region.n * tree_size);
for (i = 0; i < region.n; i++) {
struct tcg_region_tree *rt = region_trees + i * tree_size;
qemu_mutex_init(&rt->lock);
rt->tree = g_tree_new(tb_tc_cmp);
}
}
static struct tcg_region_tree *tc_ptr_to_region_tree(void *p)
{
size_t region_idx;
if (p < region.start_aligned) {
region_idx = 0;
} else {
ptrdiff_t offset = p - region.start_aligned;
if (offset > region.stride * (region.n - 1)) {
region_idx = region.n - 1;
} else {
region_idx = offset / region.stride;
}
}
return region_trees + region_idx * tree_size;
}
void tcg_tb_insert(TranslationBlock *tb)
{
struct tcg_region_tree *rt = tc_ptr_to_region_tree(tb->tc.ptr);
qemu_mutex_lock(&rt->lock);
g_tree_insert(rt->tree, &tb->tc, tb);
qemu_mutex_unlock(&rt->lock);
}
void tcg_tb_remove(TranslationBlock *tb)
{
struct tcg_region_tree *rt = tc_ptr_to_region_tree(tb->tc.ptr);
qemu_mutex_lock(&rt->lock);
g_tree_remove(rt->tree, &tb->tc);
qemu_mutex_unlock(&rt->lock);
}
/*
* Find the TB 'tb' such that
* tb->tc.ptr <= tc_ptr < tb->tc.ptr + tb->tc.size
* Return NULL if not found.
*/
TranslationBlock *tcg_tb_lookup(uintptr_t tc_ptr)
{
struct tcg_region_tree *rt = tc_ptr_to_region_tree((void *)tc_ptr);
TranslationBlock *tb;
struct tb_tc s = { .ptr = (void *)tc_ptr };
qemu_mutex_lock(&rt->lock);
tb = g_tree_lookup(rt->tree, &s);
qemu_mutex_unlock(&rt->lock);
return tb;
}
static void tcg_region_tree_lock_all(void)
{
size_t i;
for (i = 0; i < region.n; i++) {
struct tcg_region_tree *rt = region_trees + i * tree_size;
qemu_mutex_lock(&rt->lock);
}
}
static void tcg_region_tree_unlock_all(void)
{
size_t i;
for (i = 0; i < region.n; i++) {
struct tcg_region_tree *rt = region_trees + i * tree_size;
qemu_mutex_unlock(&rt->lock);
}
}
void tcg_tb_foreach(GTraverseFunc func, gpointer user_data)
{
size_t i;
tcg_region_tree_lock_all();
for (i = 0; i < region.n; i++) {
struct tcg_region_tree *rt = region_trees + i * tree_size;
g_tree_foreach(rt->tree, func, user_data);
}
tcg_region_tree_unlock_all();
}
size_t tcg_nb_tbs(void)
{
size_t nb_tbs = 0;
size_t i;
tcg_region_tree_lock_all();
for (i = 0; i < region.n; i++) {
struct tcg_region_tree *rt = region_trees + i * tree_size;
nb_tbs += g_tree_nnodes(rt->tree);
}
tcg_region_tree_unlock_all();
return nb_tbs;
}
static void tcg_region_tree_reset_all(void)
{
size_t i;
tcg_region_tree_lock_all();
for (i = 0; i < region.n; i++) {
struct tcg_region_tree *rt = region_trees + i * tree_size;
/* Increment the refcount first so that destroy acts as a reset */
g_tree_ref(rt->tree);
g_tree_destroy(rt->tree);
}
tcg_region_tree_unlock_all();
}
static void tcg_region_bounds(size_t curr_region, void **pstart, void **pend)
{
void *start, *end;
@ -380,6 +567,8 @@ void tcg_region_reset_all(void)
g_assert(!err);
}
qemu_mutex_unlock(&region.lock);
tcg_region_tree_reset_all();
}
#ifdef CONFIG_USER_ONLY
@ -496,6 +685,8 @@ void tcg_region_init(void)
g_assert(!rc);
}
tcg_region_trees_init();
/* In user-mode we support only one ctx, so do the initial allocation now */
#ifdef CONFIG_USER_ONLY
{

6
tcg/tcg.h
View File

@ -866,6 +866,12 @@ void tcg_region_reset_all(void);
size_t tcg_code_size(void);
size_t tcg_code_capacity(void);
void tcg_tb_insert(TranslationBlock *tb);
void tcg_tb_remove(TranslationBlock *tb);
TranslationBlock *tcg_tb_lookup(uintptr_t tc_ptr);
void tcg_tb_foreach(GTraverseFunc func, gpointer user_data);
size_t tcg_nb_tbs(void);
/* user-mode: Called with tb_lock held. */
static inline void *tcg_malloc(int size)
{