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[cadcdev-svn-commits] [SCM] branch master updated. 3df833497711472b1b0d8546dfcdf5031d3c6fe7
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From: kosmirror <kos...@us...> - 2025-08-05 03:05:05
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- Log -----------------------------------------------------------------
commit 3df833497711472b1b0d8546dfcdf5031d3c6fe7
Author: Falco Girgis <gyr...@gm...>
Date: Mon Aug 4 22:04:49 2025 -0500
Added flag for disabling TLS for individual threads. (#1045)
I thought of a potential optimization the other day for how we handle
TLS that could lead to some RAM savings... Say that we KNOW a thread is
just some little simple task that is never accessing any TLS variables.
If we were able to tell the kernel this is the case, we could avoid
allocating a TLS segment that will never be used for that particular
thread.
...and we already have two very good use-cases immediately within the
kernel: the reaper and idle threads are not going to be accessing any
TLS variables, yet they're getting their own copies of them allocated
upon their creation.
1) Added THD_DISABLE_TLS to kthread_flags_t for signaling to the kernel
that we're not using TLS for a particular thread.
2) Added kthread_attr_t::disable_tls flag for telling the kernel we
don't want TLS when spawning a thread and passing its attributes.
- notice it's the last member of the struct, so I don't break
backwards compat, also it's the NEGATIVE so a 0 default value
keeps the old functionality
3) Added checks to thread.c when creating and destroying threads to see
whether THD_DISABLE_TLS is used, and if so, skip TLS segment
processing.
4) Made the [reaper] and [idle] threads, by default, disable TLS.
I validated these changes by rerunning my TLS test located in:
examples/dreamcast/basic/threading/compiler_tls. Everything looks good!
-----------------------------------------------------------------------
Summary of changes:
include/kos/thread.h | 18 ++++++++++--------
kernel/thread/thread.c | 33 +++++++++++++++++++--------------
2 files changed, 29 insertions(+), 22 deletions(-)
diff --git a/include/kos/thread.h b/include/kos/thread.h
index 98457f43..581dc1af 100644
--- a/include/kos/thread.h
+++ b/include/kos/thread.h
@@ -4,7 +4,7 @@
Copyright (C) 2000, 2001, 2002, 2003 Megan Potter
Copyright (C) 2009, 2010, 2016, 2023 Lawrence Sebald
Copyright (C) 2023 Colton Pawielski
- Copyright (C) 2023, 2024 Falco Girgis
+ Copyright (C) 2023, 2024, 2025 Falco Girgis
*/
@@ -128,11 +128,12 @@ LIST_HEAD(ktlist, kthread);
@{
*/
-#define THD_DEFAULTS 0 /**< \brief Defaults: no flags */
-#define THD_USER 1 /**< \brief Thread runs in user mode */
-#define THD_QUEUED 2 /**< \brief Thread is in the run queue */
-#define THD_DETACHED 4 /**< \brief Thread is detached */
-#define THD_OWNS_STACK 8 /**< \brief Thread manages stack lifetime */
+#define THD_DEFAULTS 0x0 /**< \brief Defaults: no flags */
+#define THD_USER 0x1 /**< \brief Thread runs in user mode */
+#define THD_QUEUED 0x2 /**< \brief Thread is in the run queue */
+#define THD_DETACHED 0x4 /**< \brief Thread is detached */
+#define THD_OWNS_STACK 0x8 /**< \brief Thread manages stack lifetime */
+#define THD_DISABLE_TLS 0x10 /**< \brief Thread does not use TLS variables */
/** @} */
/** \brief Kernel thread flags type */
@@ -150,8 +151,6 @@ typedef enum kthread_state {
STATE_FINISHED = 0x0004 /**< \brief Finished execution */
} kthread_state_t;
-
-
/** \brief Structure describing one running thread.
Each thread has one of these structures assigned to it, which holds all the
@@ -289,6 +288,9 @@ typedef struct kthread_attr {
/** \brief Thread label. */
const char *label;
+
+ /** \brief 1 if the thread doesn't use thread_local variables. */
+ bool disable_tls;
} kthread_attr_t;
/** \brief kthread mode values
diff --git a/kernel/thread/thread.c b/kernel/thread/thread.c
index 374235a2..1a4b20f0 100644
--- a/kernel/thread/thread.c
+++ b/kernel/thread/thread.c
@@ -4,7 +4,7 @@
Copyright (C) 2000, 2001, 2002, 2003 Megan Potter
Copyright (C) 2010, 2016, 2023 Lawrence Sebald
Copyright (C) 2023 Colton Pawielski
- Copyright (C) 2023, 2024 Falco Girgis
+ Copyright (C) 2023, 2024, 2025 Falco Girgis
*/
#include <assert.h>
@@ -368,7 +368,7 @@ kthread_t *thd_create_ex(const kthread_attr_t *restrict attr,
kthread_t *nt = NULL;
tid_t tid;
uint32_t params[4];
- kthread_attr_t real_attr = { false, THD_STACK_SIZE, NULL, PRIO_DEFAULT, NULL };
+ kthread_attr_t real_attr = { false, THD_STACK_SIZE, NULL, PRIO_DEFAULT, NULL, false };
if(attr)
real_attr = *attr;
@@ -430,8 +430,10 @@ kthread_t *thd_create_ex(const kthread_attr_t *restrict attr,
((uint32_t)nt->stack) + nt->stack_size,
(uint32_t)thd_birth, params, 0);
- /* Create static TLS data */
- if(!arch_tls_setup_data(nt)) {
+ /* Create static TLS data if the thread hasn't disabled it. */
+ if(real_attr.disable_tls) {
+ nt->flags |= THD_DISABLE_TLS;
+ } else if(!arch_tls_setup_data(nt)) {
if(nt->flags & THD_OWNS_STACK)
free(nt->stack);
free(nt);
@@ -526,8 +528,9 @@ int thd_destroy(kthread_t *thd) {
if(thd->flags & THD_OWNS_STACK)
free(thd->stack);
- /* Free static TLS segment */
- arch_tls_destroy_data(thd);
+ /* Free static TLS segment (if it hasn't been disabled for the thread). */
+ if(!(thd->flags & THD_DISABLE_TLS))
+ arch_tls_destroy_data(thd);
/* Free the thread */
free(thd);
@@ -1004,17 +1007,19 @@ int thd_init(void) {
};
const kthread_attr_t reaper_attr = {
- .stack_size = sizeof(thd_reaper_stack),
- .stack_ptr = thd_reaper_stack,
- .prio = 1,
- .label = "[reaper]"
+ .stack_size = sizeof(thd_reaper_stack),
+ .stack_ptr = thd_reaper_stack,
+ .prio = 1,
+ .label = "[reaper]"
+ .disable_tls = true
};
const kthread_attr_t idle_attr = {
- .stack_size = sizeof(thd_idle_stack),
- .stack_ptr = thd_idle_stack,
- .prio = PRIO_MAX,
- .label = "[idle]"
+ .stack_size = sizeof(thd_idle_stack),
+ .stack_ptr = thd_idle_stack,
+ .prio = PRIO_MAX,
+ .label = "[idle]"
+ .disable_tls = true
};
kthread_t *kern;
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