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Date: Fri, 30 Sep 2016 14:35:38 +0800
From: Pan Xinhui <xinhui@...ux.vnet.ibm.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Christian Borntraeger <borntraeger@...ibm.com>,
Peter Zijlstra <peterz@...radead.org>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
linux-s390@...r.kernel.org, kvm@...r.kernel.org,
xen-devel-request@...ts.xenproject.org, benh@...nel.crashing.org,
paulus@...ba.org, mpe@...erman.id.au, mingo@...hat.com,
paulmck@...ux.vnet.ibm.com, will.deacon@....com,
kernellwp@...il.com, jgross@...e.com, pbonzini@...hat.com,
bsingharora@...il.com
Subject: Re: [PATCH v2 1/1] s390/spinlock: Provide vcpu_is_preempted
在 2016/9/30 13:52, Boqun Feng 写道:
> On Fri, Sep 30, 2016 at 12:49:52PM +0800, Pan Xinhui wrote:
>>
>>
>> 在 2016/9/29 23:51, Christian Borntraeger 写道:
>>> this implements the s390 backend for commit
>>> "kernel/sched: introduce vcpu preempted check interface"
>>> by reworking the existing smp_vcpu_scheduled into
>>> arch_vcpu_is_preempted. We can then also get rid of the
>>> local cpu_is_preempted function by moving the
>>> CIF_ENABLED_WAIT test into arch_vcpu_is_preempted.
>>>
>>> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
>>> ---
>>
>> hi, Christian
>> thanks for your patch!
>>
>>> arch/s390/include/asm/spinlock.h | 3 +++
>>> arch/s390/kernel/smp.c | 9 +++++++--
>>> arch/s390/lib/spinlock.c | 25 ++++++++-----------------
>>> 3 files changed, 18 insertions(+), 19 deletions(-)
>>>
>>> diff --git a/arch/s390/include/asm/spinlock.h b/arch/s390/include/asm/spinlock.h
>>> index 63ebf37..e16e02f 100644
>>> --- a/arch/s390/include/asm/spinlock.h
>>> +++ b/arch/s390/include/asm/spinlock.h
>>> @@ -21,6 +21,9 @@ _raw_compare_and_swap(unsigned int *lock, unsigned int old, unsigned int new)
>>> return __sync_bool_compare_and_swap(lock, old, new);
>>> }
>>>
>>> +bool arch_vcpu_is_preempted(int cpu);
>>> +#define vcpu_is_preempted arch_vcpu_is_preempted
>>> +
>>> /*
>>> * Simple spin lock operations. There are two variants, one clears IRQ's
>>> * on the local processor, one does not.
>>> diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
>>> index 7b89a75..4aadd16 100644
>>> --- a/arch/s390/kernel/smp.c
>>> +++ b/arch/s390/kernel/smp.c
>>> @@ -376,10 +376,15 @@ int smp_find_processor_id(u16 address)
>>> return -1;
>>> }
>>>
>>> -int smp_vcpu_scheduled(int cpu)
>> root@...alpine2-lp13:~/linux# git grep -wn smp_vcpu_scheduled arch/s390/
>> arch/s390/include/asm/smp.h:34:extern int smp_vcpu_scheduled(int cpu);
>> arch/s390/include/asm/smp.h:56:static inline int smp_vcpu_scheduled(int cpu) { return 1; }
>> arch/s390/kernel/smp.c:371:int smp_vcpu_scheduled(int cpu)
>> arch/s390/lib/spinlock.c:44: if (smp_vcpu_scheduled(cpu))
>>
>>> +bool arch_vcpu_is_preempted(int cpu)
>>> {
>>> - return pcpu_running(pcpu_devices + cpu);
>>> + if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
>>> + return false;
>>> + if (pcpu_running(pcpu_devices + cpu))
>>> + return false;
>> I saw smp_vcpu_scheduled() returns true always on !SMP system.
>>
>> maybe we can do somegthing silimar. like below
>>
>> #ifndef CONFIG_SMP
>> static inline bool arch_vcpu_is_preempted(int cpu) { return !test_cpu_flag_of(CIF_ENABLED_WAIT, cpu); }
>> #else
>> ...
>>
>> but I can't help thinking that if this is a!SMP system, maybe we could only
>> #ifndef CONFIG_SMP
>> static inline bool arch_vcpu_is_preempted(int cpu) { return false; }
>> #else
>
> Why do we need a vcpu_is_preempted() implementation for UP? Where will
> you use it?
>
yep, I also wonder that :)
But there is a definitaion of smp_vcpu_scheduled() for !SMP kernel.
So I am a little worried that some code has included this spinlock.h for UP kernel also.
Hi, Christian
Could you help confirms that your patch works on UP? :)
thanks
xinhui
> Regards,
> Boqun
>
>> ...
>>
>>
>> thanks
>> xinhui
>>
>>> + return true;
>>> }
>>> +EXPORT_SYMBOL(arch_vcpu_is_preempted);
>>>
>>> void smp_yield_cpu(int cpu)
>>> {
>>> diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
>>> index e5f50a7..e48a48e 100644
>>> --- a/arch/s390/lib/spinlock.c
>>> +++ b/arch/s390/lib/spinlock.c
>>> @@ -37,15 +37,6 @@ static inline void _raw_compare_and_delay(unsigned int *lock, unsigned int old)
>>> asm(".insn rsy,0xeb0000000022,%0,0,%1" : : "d" (old), "Q" (*lock));
>>> }
>>>
>>> -static inline int cpu_is_preempted(int cpu)
>>> -{
>>> - if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
>>> - return 0;
>>> - if (smp_vcpu_scheduled(cpu))
>>> - return 0;
>>> - return 1;
>>> -}
>>> -
>>> void arch_spin_lock_wait(arch_spinlock_t *lp)
>>> {
>>> unsigned int cpu = SPINLOCK_LOCKVAL;
>>> @@ -62,7 +53,7 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
>>> continue;
>>> }
>>> /* First iteration: check if the lock owner is running. */
>>> - if (first_diag && cpu_is_preempted(~owner)) {
>>> + if (first_diag && arch_vcpu_is_preempted(~owner)) {
>>> smp_yield_cpu(~owner);
>>> first_diag = 0;
>>> continue;
>>> @@ -81,7 +72,7 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
>>> * yield the CPU unconditionally. For LPAR rely on the
>>> * sense running status.
>>> */
>>> - if (!MACHINE_IS_LPAR || cpu_is_preempted(~owner)) {
>>> + if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner)) {
>>> smp_yield_cpu(~owner);
>>> first_diag = 0;
>>> }
>>> @@ -108,7 +99,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
>>> continue;
>>> }
>>> /* Check if the lock owner is running. */
>>> - if (first_diag && cpu_is_preempted(~owner)) {
>>> + if (first_diag && arch_vcpu_is_preempted(~owner)) {
>>> smp_yield_cpu(~owner);
>>> first_diag = 0;
>>> continue;
>>> @@ -127,7 +118,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
>>> * yield the CPU unconditionally. For LPAR rely on the
>>> * sense running status.
>>> */
>>> - if (!MACHINE_IS_LPAR || cpu_is_preempted(~owner)) {
>>> + if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner)) {
>>> smp_yield_cpu(~owner);
>>> first_diag = 0;
>>> }
>>> @@ -165,7 +156,7 @@ void _raw_read_lock_wait(arch_rwlock_t *rw)
>>> owner = 0;
>>> while (1) {
>>> if (count-- <= 0) {
>>> - if (owner && cpu_is_preempted(~owner))
>>> + if (owner && arch_vcpu_is_preempted(~owner))
>>> smp_yield_cpu(~owner);
>>> count = spin_retry;
>>> }
>>> @@ -211,7 +202,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw, unsigned int prev)
>>> owner = 0;
>>> while (1) {
>>> if (count-- <= 0) {
>>> - if (owner && cpu_is_preempted(~owner))
>>> + if (owner && arch_vcpu_is_preempted(~owner))
>>> smp_yield_cpu(~owner);
>>> count = spin_retry;
>>> }
>>> @@ -241,7 +232,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw)
>>> owner = 0;
>>> while (1) {
>>> if (count-- <= 0) {
>>> - if (owner && cpu_is_preempted(~owner))
>>> + if (owner && arch_vcpu_is_preempted(~owner))
>>> smp_yield_cpu(~owner);
>>> count = spin_retry;
>>> }
>>> @@ -285,7 +276,7 @@ void arch_lock_relax(unsigned int cpu)
>>> {
>>> if (!cpu)
>>> return;
>>> - if (MACHINE_IS_LPAR && !cpu_is_preempted(~cpu))
>>> + if (MACHINE_IS_LPAR && !arch_vcpu_is_preempted(~cpu))
>>> return;
>>> smp_yield_cpu(~cpu);
>>> }
>>>
>>
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