Hi Peter,
On 2018/11/6 17:06, Peter Zijlstra wrote:
> On Mon, Nov 05, 2018 at 10:49:21PM +0000, Will Deacon wrote:
>> diff --git a/include/asm-generic/bitops/lock.h
>> b/include/asm-generic/bitops/lock.h
>> index 3ae021368f48..9de8d3544630 100644
>> --- a/include/asm-generic/bitops/lock.h
>> +++ b/include/asm-generic/bitops/lock.h
>> @@ -6,6 +6,15 @@
>> #include <linux/compiler.h>
>> #include <asm/barrier.h>
>>
>> +static inline void spin_until_bit_unlock(unsigned int nr,
>> + volatile unsigned long *p)
>> +{
>> + unsigned long mask = BIT_MASK(bitnum);
>> +
>> + p += BIT_WORD(nr);
>> + smp_cond_load_relaxed(p, VAL & mask);
>> +}
>> +
>> /**
>> * test_and_set_bit_lock - Set a bit and return its old value, for lock
>> * @nr: Bit to set
>> diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
>> index bbc4730a6505..d711c62e718c 100644
>> --- a/include/linux/bit_spinlock.h
>> +++ b/include/linux/bit_spinlock.h
>> @@ -26,9 +26,7 @@ static inline void bit_spin_lock(int bitnum, unsigned long
>> *addr)
>> #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
>> while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
>> preempt_enable();
>> - do {
>> - cpu_relax();
>> - } while (test_bit(bitnum, addr));
>> + spin_until_bit_unlock(bitnum, addr);
>> preempt_disable();
>> }
>> #endif
>
> Yes, that's much better. Ideally though, we'd get rid of bit spinlocks
> that have significant enough contention for this to matter.
OK, I will send v3 to fix like the above.
Thanks,
Gao Xiang
>
>
