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Message-Id: <20220421101033.216394-11-jcmvbkbc@gmail.com>
Date: Thu, 21 Apr 2022 03:10:33 -0700
From: Max Filippov <jcmvbkbc@...il.com>
To: linux-xtensa@...ux-xtensa.org
Cc: Chris Zankel <chris@...kel.net>, linux-kernel@...r.kernel.org,
Max Filippov <jcmvbkbc@...il.com>
Subject: [PATCH v2 10/10] xtensa: support coprocessors on SMP
Current coprocessor support on xtensa only works correctly on
uniprocessor configurations. Make it work on SMP too and keep it lazy.
Make coprocessor_owner array per-CPU and move it to struct exc_table for
easy access from the fast_coprocessor exception handler. Allow task to
have live coprocessors only on single CPU, record this CPU number in the
struct thread_info::cp_owner_cpu. Change struct thread_info::cpenable
meaning to be 'coprocessors live on cp_owner_cpu'.
Introduce C-level coprocessor exception handler that flushes and
releases live coprocessors of the task taking 'coprocessor disabled'
exception and call it from the fast_coprocessor handler when the task
has live coprocessors on other CPU.
Make coprocessor_flush_all and coprocessor_release_all work correctly
when called from any CPU by sending IPI to the cp_owner_cpu. Add
function coprocessor_flush_release_all to do flush followed by release
atomically. Add function local_coprocessors_flush_release_all to flush
and release all coprocessors on the local CPU and use it to flush
coprocessor contexts from the CPU that goes offline.
Signed-off-by: Max Filippov <jcmvbkbc@...il.com>
---
Changes v1->v2:
- document rules for coprocessor context management
- clean up context management from the LKMM point of view, introduce
and document barriers
- support CPU hotplug
arch/xtensa/include/asm/coprocessor.h | 4 +-
arch/xtensa/include/asm/thread_info.h | 7 +-
arch/xtensa/include/asm/traps.h | 6 ++
arch/xtensa/kernel/asm-offsets.c | 8 +-
arch/xtensa/kernel/coprocessor.S | 122 +++++++++++++++++++-------
arch/xtensa/kernel/entry.S | 12 ++-
arch/xtensa/kernel/process.c | 112 +++++++++++++++++------
arch/xtensa/kernel/ptrace.c | 3 +-
arch/xtensa/kernel/signal.c | 3 +-
arch/xtensa/kernel/smp.c | 7 ++
arch/xtensa/kernel/traps.c | 13 ++-
11 files changed, 230 insertions(+), 67 deletions(-)
diff --git a/arch/xtensa/include/asm/coprocessor.h b/arch/xtensa/include/asm/coprocessor.h
index a360efced7e7..3b1a0d5d2169 100644
--- a/arch/xtensa/include/asm/coprocessor.h
+++ b/arch/xtensa/include/asm/coprocessor.h
@@ -142,10 +142,12 @@ typedef struct { XCHAL_CP6_SA_LIST(2) } xtregs_cp6_t
typedef struct { XCHAL_CP7_SA_LIST(2) } xtregs_cp7_t
__attribute__ ((aligned (XCHAL_CP7_SA_ALIGN)));
-extern struct thread_info* coprocessor_owner[XCHAL_CP_MAX];
+struct thread_info;
void coprocessor_flush(struct thread_info *ti, int cp_index);
void coprocessor_release_all(struct thread_info *ti);
void coprocessor_flush_all(struct thread_info *ti);
+void coprocessor_flush_release_all(struct thread_info *ti);
+void local_coprocessors_flush_release_all(void);
#endif /* XTENSA_HAVE_COPROCESSORS */
diff --git a/arch/xtensa/include/asm/thread_info.h b/arch/xtensa/include/asm/thread_info.h
index f6fcbba1d02f..52974317a6b6 100644
--- a/arch/xtensa/include/asm/thread_info.h
+++ b/arch/xtensa/include/asm/thread_info.h
@@ -52,12 +52,17 @@ struct thread_info {
__u32 cpu; /* current CPU */
__s32 preempt_count; /* 0 => preemptable,< 0 => BUG*/
- unsigned long cpenable;
#if XCHAL_HAVE_EXCLUSIVE
/* result of the most recent exclusive store */
unsigned long atomctl8;
#endif
+ /*
+ * If i-th bit is set then coprocessor state is loaded into the
+ * coprocessor i on CPU cp_owner_cpu.
+ */
+ unsigned long cpenable;
+ u32 cp_owner_cpu;
/* Allocate storage for extra user states and coprocessor states. */
#if XTENSA_HAVE_COPROCESSORS
xtregs_coprocessor_t xtregs_cp;
diff --git a/arch/xtensa/include/asm/traps.h b/arch/xtensa/include/asm/traps.h
index 514376eff58c..6f74ccc0c7ea 100644
--- a/arch/xtensa/include/asm/traps.h
+++ b/arch/xtensa/include/asm/traps.h
@@ -27,6 +27,10 @@ struct exc_table {
void *fixup;
/* For passing a parameter to fixup */
void *fixup_param;
+#if XTENSA_HAVE_COPROCESSORS
+ /* Pointers to owner struct thread_info */
+ struct thread_info *coprocessor_owner[XCHAL_CP_MAX];
+#endif
/* Fast user exception handlers */
void *fast_user_handler[EXCCAUSE_N];
/* Fast kernel exception handlers */
@@ -35,6 +39,8 @@ struct exc_table {
xtensa_exception_handler *default_handler[EXCCAUSE_N];
};
+DECLARE_PER_CPU(struct exc_table, exc_table);
+
xtensa_exception_handler *
__init trap_set_handler(int cause, xtensa_exception_handler *handler);
diff --git a/arch/xtensa/kernel/asm-offsets.c b/arch/xtensa/kernel/asm-offsets.c
index 37278e2785fb..e3b9cf4c2289 100644
--- a/arch/xtensa/kernel/asm-offsets.c
+++ b/arch/xtensa/kernel/asm-offsets.c
@@ -91,10 +91,12 @@ int main(void)
/* struct thread_info (offset from start_struct) */
DEFINE(THREAD_RA, offsetof (struct task_struct, thread.ra));
DEFINE(THREAD_SP, offsetof (struct task_struct, thread.sp));
- DEFINE(THREAD_CPENABLE, offsetof (struct thread_info, cpenable));
#if XCHAL_HAVE_EXCLUSIVE
DEFINE(THREAD_ATOMCTL8, offsetof (struct thread_info, atomctl8));
#endif
+ DEFINE(THREAD_CPENABLE, offsetof(struct thread_info, cpenable));
+ DEFINE(THREAD_CPU, offsetof(struct thread_info, cpu));
+ DEFINE(THREAD_CP_OWNER_CPU, offsetof(struct thread_info, cp_owner_cpu));
#if XTENSA_HAVE_COPROCESSORS
DEFINE(THREAD_XTREGS_CP0, offsetof(struct thread_info, xtregs_cp.cp0));
DEFINE(THREAD_XTREGS_CP1, offsetof(struct thread_info, xtregs_cp.cp1));
@@ -137,6 +139,10 @@ int main(void)
DEFINE(EXC_TABLE_DOUBLE_SAVE, offsetof(struct exc_table, double_save));
DEFINE(EXC_TABLE_FIXUP, offsetof(struct exc_table, fixup));
DEFINE(EXC_TABLE_PARAM, offsetof(struct exc_table, fixup_param));
+#if XTENSA_HAVE_COPROCESSORS
+ DEFINE(EXC_TABLE_COPROCESSOR_OWNER,
+ offsetof(struct exc_table, coprocessor_owner));
+#endif
DEFINE(EXC_TABLE_FAST_USER,
offsetof(struct exc_table, fast_user_handler));
DEFINE(EXC_TABLE_FAST_KERNEL,
diff --git a/arch/xtensa/kernel/coprocessor.S b/arch/xtensa/kernel/coprocessor.S
index 95412409c49e..ef33e76e07d8 100644
--- a/arch/xtensa/kernel/coprocessor.S
+++ b/arch/xtensa/kernel/coprocessor.S
@@ -19,6 +19,26 @@
#include <asm/current.h>
#include <asm/regs.h>
+/*
+ * Rules for coprocessor state manipulation on SMP:
+ *
+ * - a task may have live coprocessors only on one CPU.
+ *
+ * - whether coprocessor context of task T is live on some CPU is
+ * denoted by T's thread_info->cpenable.
+ *
+ * - non-zero thread_info->cpenable means that thread_info->cp_owner_cpu
+ * is valid in the T's thread_info. Zero thread_info->cpenable means that
+ * coprocessor context is valid in the T's thread_info.
+ *
+ * - if a coprocessor context of task T is live on CPU X, only CPU X changes
+ * T's thread_info->cpenable, cp_owner_cpu and coprocessor save area.
+ * This is done by making sure that for the task T with live coprocessor
+ * on CPU X cpenable SR is 0 when T runs on any other CPU Y.
+ * When fast_coprocessor exception is taken on CPU Y it goes to the
+ * C-level do_coprocessor that uses IPI to make CPU X flush T's coprocessors.
+ */
+
#if XTENSA_HAVE_COPROCESSORS
/*
@@ -101,9 +121,37 @@
ENTRY(fast_coprocessor)
+ s32i a3, a2, PT_AREG3
+
+#ifdef CONFIG_SMP
+ /*
+ * Check if any coprocessor context is live on another CPU
+ * and if so go through the C-level coprocessor exception handler
+ * to flush it to memory.
+ */
+ GET_THREAD_INFO (a0, a2)
+ l32i a3, a0, THREAD_CPENABLE
+ beqz a3, .Lload_local
+
+ /*
+ * Pairs with smp_wmb in local_coprocessor_release_all
+ * and with both memws below.
+ */
+ memw
+ l32i a3, a0, THREAD_CPU
+ l32i a0, a0, THREAD_CP_OWNER_CPU
+ beq a0, a3, .Lload_local
+
+ rsr a0, ps
+ l32i a3, a2, PT_AREG3
+ bbci.l a0, PS_UM_BIT, 1f
+ call0 user_exception
+1: call0 kernel_exception
+#endif
+
/* Save remaining registers a1-a3 and SAR */
- s32i a3, a2, PT_AREG3
+.Lload_local:
rsr a3, sar
s32i a1, a2, PT_AREG1
s32i a3, a2, PT_SAR
@@ -117,6 +165,9 @@ ENTRY(fast_coprocessor)
s32i a5, a1, PT_AREG5
s32i a6, a1, PT_AREG6
s32i a7, a1, PT_AREG7
+ s32i a8, a1, PT_AREG8
+ s32i a9, a1, PT_AREG9
+ s32i a10, a1, PT_AREG10
/* Find coprocessor number. Subtract first CP EXCCAUSE from EXCCAUSE */
@@ -139,51 +190,66 @@ ENTRY(fast_coprocessor)
addx8 a7, a3, a7
addx4 a7, a3, a7
- /* Retrieve previous owner. (a3 still holds CP number) */
+ /* Retrieve previous owner (a8). */
- movi a0, coprocessor_owner # list of owners
+ rsr a0, excsave1 # exc_table
addx4 a0, a3, a0 # entry for CP
- l32i a4, a0, 0
+ l32i a8, a0, EXC_TABLE_COPROCESSOR_OWNER
- beqz a4, 1f # skip 'save' if no previous owner
+ /* Set new owner (a9). */
- /* Disable coprocessor for previous owner. (a2 = 1 << CP number) */
+ GET_THREAD_INFO (a9, a1)
+ l32i a4, a9, THREAD_CPU
+ s32i a9, a0, EXC_TABLE_COPROCESSOR_OWNER
+ s32i a4, a9, THREAD_CP_OWNER_CPU
- l32i a5, a4, THREAD_CPENABLE
- xor a5, a5, a2 # (1 << cp-id) still in a2
- s32i a5, a4, THREAD_CPENABLE
+ /*
+ * Enable coprocessor for the new owner. (a2 = 1 << CP number)
+ * This can be done before loading context into the coprocessor.
+ */
+ l32i a4, a9, THREAD_CPENABLE
+ or a4, a4, a2
/*
- * Get context save area and call save routine.
- * (a4 still holds previous owner (thread_info), a3 CP number)
+ * Make sure THREAD_CP_OWNER_CPU is in memory before updating
+ * THREAD_CPENABLE
*/
+ memw # (2)
+ s32i a4, a9, THREAD_CPENABLE
- l32i a2, a7, CP_REGS_TAB_OFFSET
- l32i a3, a7, CP_REGS_TAB_SAVE
- add a2, a2, a4
- callx0 a3
+ beqz a8, 1f # skip 'save' if no previous owner
- /* Note that only a0 and a1 were preserved. */
+ /* Disable coprocessor for previous owner. (a2 = 1 << CP number) */
- rsr a3, exccause
- addi a3, a3, -EXCCAUSE_COPROCESSOR0_DISABLED
- movi a0, coprocessor_owner
- addx4 a0, a3, a0
+ l32i a10, a8, THREAD_CPENABLE
+ xor a10, a10, a2
- /* Set new 'owner' (a0 points to the CP owner, a3 contains the CP nr) */
+ /* Get context save area and call save routine. */
-1: GET_THREAD_INFO (a4, a1)
- s32i a4, a0, 0
+ l32i a2, a7, CP_REGS_TAB_OFFSET
+ l32i a3, a7, CP_REGS_TAB_SAVE
+ add a2, a2, a8
+ callx0 a3
+ /*
+ * Make sure coprocessor context and THREAD_CP_OWNER_CPU are in memory
+ * before updating THREAD_CPENABLE
+ */
+ memw # (3)
+ s32i a10, a8, THREAD_CPENABLE
+1:
/* Get context save area and call load routine. */
l32i a2, a7, CP_REGS_TAB_OFFSET
l32i a3, a7, CP_REGS_TAB_LOAD
- add a2, a2, a4
+ add a2, a2, a9
callx0 a3
/* Restore all registers and return from exception handler. */
+ l32i a10, a1, PT_AREG10
+ l32i a9, a1, PT_AREG9
+ l32i a8, a1, PT_AREG8
l32i a7, a1, PT_AREG7
l32i a6, a1, PT_AREG6
l32i a5, a1, PT_AREG5
@@ -233,12 +299,4 @@ ENTRY(coprocessor_flush)
ENDPROC(coprocessor_flush)
- .data
-
-ENTRY(coprocessor_owner)
-
- .fill XCHAL_CP_MAX, 4, 0
-
-END(coprocessor_owner)
-
#endif /* XTENSA_HAVE_COPROCESSORS */
diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index f2c789a5a92a..3255d4f61844 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -2071,8 +2071,16 @@ ENTRY(_switch_to)
#if (XTENSA_HAVE_COPROCESSORS || XTENSA_HAVE_IO_PORTS)
l32i a3, a5, THREAD_CPENABLE
- xsr a3, cpenable
- s32i a3, a4, THREAD_CPENABLE
+#ifdef CONFIG_SMP
+ beqz a3, 1f
+ memw # pairs with memw (2) in fast_coprocessor
+ l32i a6, a5, THREAD_CP_OWNER_CPU
+ l32i a7, a5, THREAD_CPU
+ beq a6, a7, 1f # load 0 into CPENABLE if current CPU is not the owner
+ movi a3, 0
+1:
+#endif
+ wsr a3, cpenable
#endif
#if XCHAL_HAVE_EXCLUSIVE
diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c
index e8bfbca5f001..7e38292dd07a 100644
--- a/arch/xtensa/kernel/process.c
+++ b/arch/xtensa/kernel/process.c
@@ -47,6 +47,7 @@
#include <asm/asm-offsets.h>
#include <asm/regs.h>
#include <asm/hw_breakpoint.h>
+#include <asm/traps.h>
extern void ret_from_fork(void);
extern void ret_from_kernel_thread(void);
@@ -63,52 +64,114 @@ EXPORT_SYMBOL(__stack_chk_guard);
#if XTENSA_HAVE_COPROCESSORS
-void coprocessor_release_all(struct thread_info *ti)
+void local_coprocessors_flush_release_all(void)
{
- unsigned long cpenable;
- int i;
+ struct thread_info **coprocessor_owner;
+ struct thread_info *unique_owner[XCHAL_CP_MAX];
+ int n = 0;
+ int i, j;
- /* Make sure we don't switch tasks during this operation. */
+ coprocessor_owner = this_cpu_ptr(&exc_table)->coprocessor_owner;
+ xtensa_set_sr(XCHAL_CP_MASK, cpenable);
- preempt_disable();
+ for (i = 0; i < XCHAL_CP_MAX; i++) {
+ struct thread_info *ti = coprocessor_owner[i];
- /* Walk through all cp owners and release it for the requested one. */
+ if (ti) {
+ coprocessor_flush(ti, i);
- cpenable = ti->cpenable;
+ for (j = 0; j < n; j++)
+ if (unique_owner[j] == ti)
+ break;
+ if (j == n)
+ unique_owner[n++] = ti;
- for (i = 0; i < XCHAL_CP_MAX; i++) {
- if (coprocessor_owner[i] == ti) {
- coprocessor_owner[i] = 0;
- cpenable &= ~(1 << i);
+ coprocessor_owner[i] = NULL;
}
}
+ for (i = 0; i < n; i++) {
+ /* pairs with memw (1) in fast_coprocessor and memw in switch_to */
+ smp_wmb();
+ unique_owner[i]->cpenable = 0;
+ }
+ xtensa_set_sr(0, cpenable);
+}
- ti->cpenable = cpenable;
+static void local_coprocessor_release_all(void *info)
+{
+ struct thread_info *ti = info;
+ struct thread_info **coprocessor_owner;
+ int i;
+
+ coprocessor_owner = this_cpu_ptr(&exc_table)->coprocessor_owner;
+
+ /* Walk through all cp owners and release it for the requested one. */
+
+ for (i = 0; i < XCHAL_CP_MAX; i++) {
+ if (coprocessor_owner[i] == ti)
+ coprocessor_owner[i] = NULL;
+ }
+ /* pairs with memw (1) in fast_coprocessor and memw in switch_to */
+ smp_wmb();
+ ti->cpenable = 0;
if (ti == current_thread_info())
xtensa_set_sr(0, cpenable);
+}
- preempt_enable();
+void coprocessor_release_all(struct thread_info *ti)
+{
+ if (ti->cpenable) {
+ /* pairs with memw (2) in fast_coprocessor */
+ smp_rmb();
+ smp_call_function_single(ti->cp_owner_cpu,
+ local_coprocessor_release_all,
+ ti, true);
+ }
}
-void coprocessor_flush_all(struct thread_info *ti)
+static void local_coprocessor_flush_all(void *info)
{
- unsigned long cpenable, old_cpenable;
+ struct thread_info *ti = info;
+ struct thread_info **coprocessor_owner;
+ unsigned long old_cpenable;
int i;
- preempt_disable();
-
- old_cpenable = xtensa_get_sr(cpenable);
- cpenable = ti->cpenable;
- xtensa_set_sr(cpenable, cpenable);
+ coprocessor_owner = this_cpu_ptr(&exc_table)->coprocessor_owner;
+ old_cpenable = xtensa_xsr(ti->cpenable, cpenable);
for (i = 0; i < XCHAL_CP_MAX; i++) {
- if ((cpenable & 1) != 0 && coprocessor_owner[i] == ti)
+ if (coprocessor_owner[i] == ti)
coprocessor_flush(ti, i);
- cpenable >>= 1;
}
xtensa_set_sr(old_cpenable, cpenable);
+}
- preempt_enable();
+void coprocessor_flush_all(struct thread_info *ti)
+{
+ if (ti->cpenable) {
+ /* pairs with memw (2) in fast_coprocessor */
+ smp_rmb();
+ smp_call_function_single(ti->cp_owner_cpu,
+ local_coprocessor_flush_all,
+ ti, true);
+ }
+}
+
+static void local_coprocessor_flush_release_all(void *info)
+{
+ local_coprocessor_flush_all(info);
+ local_coprocessor_release_all(info);
+}
+
+void coprocessor_flush_release_all(struct thread_info *ti)
+{
+ if (ti->cpenable) {
+ /* pairs with memw (2) in fast_coprocessor */
+ smp_rmb();
+ smp_call_function_single(ti->cp_owner_cpu,
+ local_coprocessor_flush_release_all,
+ ti, true);
+ }
}
#endif
@@ -140,8 +203,7 @@ void flush_thread(void)
{
#if XTENSA_HAVE_COPROCESSORS
struct thread_info *ti = current_thread_info();
- coprocessor_flush_all(ti);
- coprocessor_release_all(ti);
+ coprocessor_flush_release_all(ti);
#endif
flush_ptrace_hw_breakpoint(current);
}
diff --git a/arch/xtensa/kernel/ptrace.c b/arch/xtensa/kernel/ptrace.c
index 323c678a691f..22cdaa6729d3 100644
--- a/arch/xtensa/kernel/ptrace.c
+++ b/arch/xtensa/kernel/ptrace.c
@@ -171,8 +171,7 @@ static int tie_set(struct task_struct *target,
#if XTENSA_HAVE_COPROCESSORS
/* Flush all coprocessors before we overwrite them. */
- coprocessor_flush_all(ti);
- coprocessor_release_all(ti);
+ coprocessor_flush_release_all(ti);
ti->xtregs_cp.cp0 = newregs->cp0;
ti->xtregs_cp.cp1 = newregs->cp1;
ti->xtregs_cp.cp2 = newregs->cp2;
diff --git a/arch/xtensa/kernel/signal.c b/arch/xtensa/kernel/signal.c
index 6f68649e86ba..c9ffd42db873 100644
--- a/arch/xtensa/kernel/signal.c
+++ b/arch/xtensa/kernel/signal.c
@@ -162,8 +162,7 @@ setup_sigcontext(struct rt_sigframe __user *frame, struct pt_regs *regs)
return err;
#if XTENSA_HAVE_COPROCESSORS
- coprocessor_flush_all(ti);
- coprocessor_release_all(ti);
+ coprocessor_flush_release_all(ti);
err |= __copy_to_user(&frame->xtregs.cp, &ti->xtregs_cp,
sizeof (frame->xtregs.cp));
#endif
diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
index ed7c188ebedc..e861ce76ad38 100644
--- a/arch/xtensa/kernel/smp.c
+++ b/arch/xtensa/kernel/smp.c
@@ -30,6 +30,7 @@
#include <linux/thread_info.h>
#include <asm/cacheflush.h>
+#include <asm/coprocessor.h>
#include <asm/kdebug.h>
#include <asm/mmu_context.h>
#include <asm/mxregs.h>
@@ -273,6 +274,12 @@ int __cpu_disable(void)
*/
set_cpu_online(cpu, false);
+#if XTENSA_HAVE_COPROCESSORS
+ /*
+ * Flush coprocessor contexts that are active on the current CPU.
+ */
+ local_coprocessors_flush_release_all();
+#endif
/*
* OK - migrate IRQs away from this CPU
*/
diff --git a/arch/xtensa/kernel/traps.c b/arch/xtensa/kernel/traps.c
index 62c497605128..138a86fbe9d7 100644
--- a/arch/xtensa/kernel/traps.c
+++ b/arch/xtensa/kernel/traps.c
@@ -57,6 +57,9 @@ static void do_nmi(struct pt_regs *regs);
static void do_unaligned_user(struct pt_regs *regs);
#endif
static void do_multihit(struct pt_regs *regs);
+#if XTENSA_HAVE_COPROCESSORS
+static void do_coprocessor(struct pt_regs *regs);
+#endif
static void do_debug(struct pt_regs *regs);
/*
@@ -69,7 +72,8 @@ static void do_debug(struct pt_regs *regs);
#define USER 0x02
#define COPROCESSOR(x) \
-{ EXCCAUSE_COPROCESSOR ## x ## _DISABLED, USER|KRNL, fast_coprocessor }
+{ EXCCAUSE_COPROCESSOR ## x ## _DISABLED, USER|KRNL, fast_coprocessor },\
+{ EXCCAUSE_COPROCESSOR ## x ## _DISABLED, 0, do_coprocessor }
typedef struct {
int cause;
@@ -327,6 +331,13 @@ static void do_unaligned_user(struct pt_regs *regs)
}
#endif
+#if XTENSA_HAVE_COPROCESSORS
+static void do_coprocessor(struct pt_regs *regs)
+{
+ coprocessor_flush_release_all(current_thread_info());
+}
+#endif
+
/* Handle debug events.
* When CONFIG_HAVE_HW_BREAKPOINT is on this handler is called with
* preemption disabled to avoid rescheduling and keep mapping of hardware
--
2.30.2
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