s390/preempt: move preempt_count to the lowcore

Convert s390 to use a field in the struct lowcore for the CPU
preemption count. It is a bit cheaper to access a lowcore field
compared to a thread_info variable and it removes the depencency
on a task related structure.

bloat-o-meter on the vmlinux image for the default configuration
(CONFIG_PREEMPT_NONE=y) reports a small reduction in text size:

add/remove: 0/0 grow/shrink: 18/578 up/down: 228/-5448 (-5220)

A larger improvement is achieved with the default configuration
but with CONFIG_PREEMPT=y and CONFIG_DEBUG_PREEMPT=n:

add/remove: 2/6 grow/shrink: 59/4477 up/down: 1618/-228762 (-227144)

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index 7b93b78f423c667315f7d963178217937858936a..1df1e6215e85ad9e1d565c9463c02530fe85917b 100644 (file)
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -126,7 +126,8 @@ struct lowcore {
        __u64   percpu_offset;                  /* 0x0378 */
        __u64   vdso_per_cpu_data;              /* 0x0380 */
        __u64   machine_flags;                  /* 0x0388 */
-       __u8    pad_0x0390[0x0398-0x0390];      /* 0x0390 */
+       __u32   preempt_count;                  /* 0x0390 */
+       __u8    pad_0x0394[0x0398-0x0394];      /* 0x0394 */
        __u64   gmap;                           /* 0x0398 */
        __u32   spinlock_lockval;               /* 0x03a0 */
        __u32   fpu_flags;                      /* 0x03a4 */

diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h
new file mode 100644 (file)
index 0000000..b0776b2
--- /dev/null
+++ b/arch/s390/include/asm/preempt.h
@@ -0,0 +1,137 @@
+#ifndef __ASM_PREEMPT_H
+#define __ASM_PREEMPT_H
+
+#include <asm/current.h>
+#include <linux/thread_info.h>
+#include <asm/atomic_ops.h>
+
+#ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
+
+#define PREEMPT_ENABLED        (0 + PREEMPT_NEED_RESCHED)
+
+static inline int preempt_count(void)
+{
+       return READ_ONCE(S390_lowcore.preempt_count) & ~PREEMPT_NEED_RESCHED;
+}
+
+static inline void preempt_count_set(int pc)
+{
+       int old, new;
+
+       do {
+               old = READ_ONCE(S390_lowcore.preempt_count);
+               new = (old & PREEMPT_NEED_RESCHED) |
+                       (pc & ~PREEMPT_NEED_RESCHED);
+       } while (__atomic_cmpxchg(&S390_lowcore.preempt_count,
+                                 old, new) != old);
+}
+
+#define init_task_preempt_count(p)     do { } while (0)
+
+#define init_idle_preempt_count(p, cpu)        do { \
+       S390_lowcore.preempt_count = PREEMPT_ENABLED; \
+} while (0)
+
+static inline void set_preempt_need_resched(void)
+{
+       __atomic_and(~PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);
+}
+
+static inline void clear_preempt_need_resched(void)
+{
+       __atomic_or(PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);
+}
+
+static inline bool test_preempt_need_resched(void)
+{
+       return !(READ_ONCE(S390_lowcore.preempt_count) & PREEMPT_NEED_RESCHED);
+}
+
+static inline void __preempt_count_add(int val)
+{
+       if (__builtin_constant_p(val) && (val >= -128) && (val <= 127))
+               __atomic_add_const(val, &S390_lowcore.preempt_count);
+       else
+               __atomic_add(val, &S390_lowcore.preempt_count);
+}
+
+static inline void __preempt_count_sub(int val)
+{
+       __preempt_count_add(-val);
+}
+
+static inline bool __preempt_count_dec_and_test(void)
+{
+       return __atomic_add(-1, &S390_lowcore.preempt_count) == 1;
+}
+
+static inline bool should_resched(int preempt_offset)
+{
+       return unlikely(READ_ONCE(S390_lowcore.preempt_count) ==
+                       preempt_offset);
+}
+
+#else /* CONFIG_HAVE_MARCH_Z196_FEATURES */
+
+#define PREEMPT_ENABLED        (0)
+
+static inline int preempt_count(void)
+{
+       return READ_ONCE(S390_lowcore.preempt_count);
+}
+
+static inline void preempt_count_set(int pc)
+{
+       S390_lowcore.preempt_count = pc;
+}
+
+#define init_task_preempt_count(p)     do { } while (0)
+
+#define init_idle_preempt_count(p, cpu)        do { \
+       S390_lowcore.preempt_count = PREEMPT_ENABLED; \
+} while (0)
+
+static inline void set_preempt_need_resched(void)
+{
+}
+
+static inline void clear_preempt_need_resched(void)
+{
+}
+
+static inline bool test_preempt_need_resched(void)
+{
+       return false;
+}
+
+static inline void __preempt_count_add(int val)
+{
+       S390_lowcore.preempt_count += val;
+}
+
+static inline void __preempt_count_sub(int val)
+{
+       S390_lowcore.preempt_count -= val;
+}
+
+static inline bool __preempt_count_dec_and_test(void)
+{
+       return !--S390_lowcore.preempt_count && tif_need_resched();
+}
+
+static inline bool should_resched(int preempt_offset)
+{
+       return unlikely(preempt_count() == preempt_offset &&
+                       tif_need_resched());
+}
+
+#endif /* CONFIG_HAVE_MARCH_Z196_FEATURES */
+
+#ifdef CONFIG_PREEMPT
+extern asmlinkage void preempt_schedule(void);
+#define __preempt_schedule() preempt_schedule()
+extern asmlinkage void preempt_schedule_notrace(void);
+#define __preempt_schedule_notrace() preempt_schedule_notrace()
+#endif /* CONFIG_PREEMPT */
+
+#endif /* __ASM_PREEMPT_H */

diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index f15c0398c3637ed49083ad4334c2b2b34e7e591c..933794150e5b7b886c6d6a2b69a70cf1544eaf54 100644 (file)
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -34,7 +34,6 @@ struct thread_info {
        unsigned long           flags;          /* low level flags */
        unsigned long           sys_call_table; /* System call table address */
        unsigned int            cpu;            /* current CPU */
-       int                     preempt_count;  /* 0 => preemptable, <0 => BUG */
        unsigned int            system_call;
        __u64                   user_timer;
        __u64                   system_timer;
@@ -49,7 +48,6 @@ struct thread_info {
        .task           = &tsk,                 \
        .flags          = 0,                    \
        .cpu            = 0,                    \
-       .preempt_count  = INIT_PREEMPT_COUNT,   \
 }
 
 #define init_thread_info       (init_thread_union.thread_info)

diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index ec16cec6bcd449dc3acd892f72f05b0d18d54722..6be10e490982cc56f460df73440e09dbac8e097f 100644 (file)
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -43,7 +43,6 @@ int main(void)
        OFFSET(__TI_flags, thread_info, flags);
        OFFSET(__TI_sysc_table, thread_info, sys_call_table);
        OFFSET(__TI_cpu, thread_info, cpu);
-       OFFSET(__TI_precount, thread_info, preempt_count);
        OFFSET(__TI_user_timer, thread_info, user_timer);
        OFFSET(__TI_system_timer, thread_info, system_timer);
        OFFSET(__TI_last_break, thread_info, last_break);
@@ -175,6 +174,7 @@ int main(void)
        OFFSET(__LC_PERCPU_OFFSET, lowcore, percpu_offset);
        OFFSET(__LC_VDSO_PER_CPU, lowcore, vdso_per_cpu_data);
        OFFSET(__LC_MACHINE_FLAGS, lowcore, machine_flags);
+       OFFSET(__LC_PREEMPT_COUNT, lowcore, preempt_count);
        OFFSET(__LC_GMAP, lowcore, gmap);
        OFFSET(__LC_PASTE, lowcore, paste);
        /* software defined ABI-relevant lowcore locations 0xe00 - 0xe20 */

diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 39d03a7a33542c9ca944aaae6823a50aeada1a3d..9cd85adaa7c1473172ff18c81c8a2ae953e0beae 100644 (file)
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -293,6 +293,7 @@ static noinline __init void setup_lowcore_early(void)
        psw.addr = (unsigned long) s390_base_pgm_handler;
        S390_lowcore.program_new_psw = psw;
        s390_base_pgm_handler_fn = early_pgm_check_handler;
+       S390_lowcore.preempt_count = INIT_PREEMPT_COUNT;
 }
 
 static noinline __init void setup_facility_list(void)

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 49a30737addef4103184ad92907b6f1f5b911bfa..3f4a1638a7005fa6e15abdab4a791e3803711e07 100644 (file)
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -626,7 +626,7 @@ ENTRY(io_int_handler)
        jo      .Lio_work_user          # yes -> do resched & signal
 #ifdef CONFIG_PREEMPT
        # check for preemptive scheduling
-       icm     %r0,15,__TI_precount(%r12)
+       icm     %r0,15,__LC_PREEMPT_COUNT
        jnz     .Lio_restore            # preemption is disabled
        TSTMSK  __TI_flags(%r12),_TIF_NEED_RESCHED
        jno     .Lio_restore

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 7f7ba5f23f130fae0639b44af7e93c84ed85a654..268d6c1b651faa600d1a3912471af779f73aca99 100644 (file)
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -333,6 +333,7 @@ static void __init setup_lowcore(void)
        lc->thread_info = (unsigned long) &init_thread_union;
        lc->lpp = LPP_MAGIC;
        lc->machine_flags = S390_lowcore.machine_flags;
+       lc->preempt_count = S390_lowcore.preempt_count;
        lc->stfl_fac_list = S390_lowcore.stfl_fac_list;
        memcpy(lc->stfle_fac_list, S390_lowcore.stfle_fac_list,
               MAX_FACILITY_BIT/8);

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 661d9fe63c430ca5f0214ada7227b6b727796dc7..d1faae5cdd122bbfefdfb18ca9874c3ed1c55952 100644 (file)
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -733,6 +733,7 @@ block:
                         * return to userspace schedule() to block. */
                        __set_current_state(TASK_UNINTERRUPTIBLE);
                        set_tsk_need_resched(tsk);
+                       set_preempt_need_resched();
                }
        }
 out: