Commit a9d107fa0e for qemu.org
commit a9d107fa0eacf6c999c042b276e54a7058ae0bf9
Author: Richard Henderson <richard.henderson@linaro.org>
Date: Fri Apr 4 16:30:57 2025 -0700
tcg: Pass max_threads not max_cpus to tcg_init
In effect, hoist the check for mttcg from tcg_n_regions()
to tcg_init_machine().
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
index a5a1fd6a11..3efc7350eb 100644
--- a/accel/tcg/tcg-all.c
+++ b/accel/tcg/tcg-all.c
@@ -103,18 +103,20 @@ bool one_insn_per_tb;
static int tcg_init_machine(MachineState *ms)
{
TCGState *s = TCG_STATE(current_accel());
-#ifdef CONFIG_USER_ONLY
- unsigned max_cpus = 1;
-#else
- unsigned max_cpus = ms->smp.max_cpus;
-#endif
+ unsigned max_threads = 1;
tcg_allowed = true;
mttcg_enabled = s->mttcg_enabled;
page_init();
tb_htable_init();
- tcg_init(s->tb_size * MiB, s->splitwx_enabled, max_cpus);
+
+#ifndef CONFIG_USER_ONLY
+ if (mttcg_enabled) {
+ max_threads = ms->smp.max_cpus;
+ }
+#endif
+ tcg_init(s->tb_size * MiB, s->splitwx_enabled, max_threads);
#if defined(CONFIG_SOFTMMU)
/*
diff --git a/include/tcg/startup.h b/include/tcg/startup.h
index f71305765c..95f574af2b 100644
--- a/include/tcg/startup.h
+++ b/include/tcg/startup.h
@@ -29,12 +29,12 @@
* tcg_init: Initialize the TCG runtime
* @tb_size: translation buffer size
* @splitwx: use separate rw and rx mappings
- * @max_cpus: number of vcpus in system mode
+ * @max_threads: number of vcpu threads in system mode
*
* Allocate and initialize TCG resources, especially the JIT buffer.
- * In user-only mode, @max_cpus is unused.
+ * In user-only mode, @max_threads is unused.
*/
-void tcg_init(size_t tb_size, int splitwx, unsigned max_cpus);
+void tcg_init(size_t tb_size, int splitwx, unsigned max_threads);
/**
* tcg_register_thread: Register this thread with the TCG runtime
diff --git a/tcg/region.c b/tcg/region.c
index 478ec051c4..7ea0b37a84 100644
--- a/tcg/region.c
+++ b/tcg/region.c
@@ -422,7 +422,7 @@ void tcg_region_reset_all(void)
tcg_region_tree_reset_all();
}
-static size_t tcg_n_regions(size_t tb_size, unsigned max_cpus)
+static size_t tcg_n_regions(size_t tb_size, unsigned max_threads)
{
#ifdef CONFIG_USER_ONLY
return 1;
@@ -431,24 +431,25 @@ static size_t tcg_n_regions(size_t tb_size, unsigned max_cpus)
/*
* It is likely that some vCPUs will translate more code than others,
- * so we first try to set more regions than max_cpus, with those regions
+ * so we first try to set more regions than threads, with those regions
* being of reasonable size. If that's not possible we make do by evenly
* dividing the code_gen_buffer among the vCPUs.
+ *
+ * Use a single region if all we have is one vCPU thread.
*/
- /* Use a single region if all we have is one vCPU thread */
- if (max_cpus == 1 || !qemu_tcg_mttcg_enabled()) {
+ if (max_threads == 1) {
return 1;
}
/*
- * Try to have more regions than max_cpus, with each region being >= 2 MB.
+ * Try to have more regions than threads, with each region being >= 2 MB.
* If we can't, then just allocate one region per vCPU thread.
*/
n_regions = tb_size / (2 * MiB);
- if (n_regions <= max_cpus) {
- return max_cpus;
+ if (n_regions <= max_threads) {
+ return max_threads;
}
- return MIN(n_regions, max_cpus * 8);
+ return MIN(n_regions, max_threads * 8);
#endif
}
@@ -731,11 +732,7 @@ static int alloc_code_gen_buffer(size_t size, int splitwx, Error **errp)
* and then assigning regions to TCG threads so that the threads can translate
* code in parallel without synchronization.
*
- * In system-mode the number of TCG threads is bounded by max_cpus, so we use at
- * least max_cpus regions in MTTCG. In !MTTCG we use a single region.
- * Note that the TCG options from the command-line (i.e. -accel accel=tcg,[...])
- * must have been parsed before calling this function, since it calls
- * qemu_tcg_mttcg_enabled().
+ * In system-mode the number of TCG threads is bounded by max_threads,
*
* In user-mode we use a single region. Having multiple regions in user-mode
* is not supported, because the number of vCPU threads (recall that each thread
@@ -749,7 +746,7 @@ static int alloc_code_gen_buffer(size_t size, int splitwx, Error **errp)
* in practice. Multi-threaded guests share most if not all of their translated
* code, which makes parallel code generation less appealing than in system-mode
*/
-void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus)
+void tcg_region_init(size_t tb_size, int splitwx, unsigned max_threads)
{
const size_t page_size = qemu_real_host_page_size();
size_t region_size;
@@ -787,7 +784,7 @@ void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus)
* As a result of this we might end up with a few extra pages at the end of
* the buffer; we will assign those to the last region.
*/
- region.n = tcg_n_regions(tb_size, max_cpus);
+ region.n = tcg_n_regions(tb_size, max_threads);
region_size = tb_size / region.n;
region_size = QEMU_ALIGN_DOWN(region_size, page_size);
diff --git a/tcg/tcg-internal.h b/tcg/tcg-internal.h
index a648ee7a0e..ff85fb23fa 100644
--- a/tcg/tcg-internal.h
+++ b/tcg/tcg-internal.h
@@ -34,7 +34,7 @@ extern TCGContext **tcg_ctxs;
extern unsigned int tcg_cur_ctxs;
extern unsigned int tcg_max_ctxs;
-void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus);
+void tcg_region_init(size_t tb_size, int splitwx, unsigned max_threads);
bool tcg_region_alloc(TCGContext *s);
void tcg_region_initial_alloc(TCGContext *s);
void tcg_region_prologue_set(TCGContext *s);
diff --git a/tcg/tcg.c b/tcg/tcg.c
index dfd48b8264..ec7f6743d7 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -1499,7 +1499,7 @@ static void process_constraint_sets(void);
static TCGTemp *tcg_global_reg_new_internal(TCGContext *s, TCGType type,
TCGReg reg, const char *name);
-static void tcg_context_init(unsigned max_cpus)
+static void tcg_context_init(unsigned max_threads)
{
TCGContext *s = &tcg_init_ctx;
int n, i;
@@ -1538,15 +1538,15 @@ static void tcg_context_init(unsigned max_cpus)
* In user-mode we simply share the init context among threads, since we
* use a single region. See the documentation tcg_region_init() for the
* reasoning behind this.
- * In system-mode we will have at most max_cpus TCG threads.
+ * In system-mode we will have at most max_threads TCG threads.
*/
#ifdef CONFIG_USER_ONLY
tcg_ctxs = &tcg_ctx;
tcg_cur_ctxs = 1;
tcg_max_ctxs = 1;
#else
- tcg_max_ctxs = max_cpus;
- tcg_ctxs = g_new0(TCGContext *, max_cpus);
+ tcg_max_ctxs = max_threads;
+ tcg_ctxs = g_new0(TCGContext *, max_threads);
#endif
tcg_debug_assert(!tcg_regset_test_reg(s->reserved_regs, TCG_AREG0));
@@ -1554,10 +1554,10 @@ static void tcg_context_init(unsigned max_cpus)
tcg_env = temp_tcgv_ptr(ts);
}
-void tcg_init(size_t tb_size, int splitwx, unsigned max_cpus)
+void tcg_init(size_t tb_size, int splitwx, unsigned max_threads)
{
- tcg_context_init(max_cpus);
- tcg_region_init(tb_size, splitwx, max_cpus);
+ tcg_context_init(max_threads);
+ tcg_region_init(tb_size, splitwx, max_threads);
}
/*