From: Gao Xiang <gaoxiang25@huawei.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Philippe Ombredanne <pombredanne@nexb.com>,
Kate Stewart <kstewart@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
<linux-kernel@vger.kernel.org>, Miao Xie <miaoxie@huawei.com>,
Chao Yu <chao@kernel.org>
Subject: Re: [PATCH v2] bit_spinlock: introduce smp_cond_load_relaxed
Date: Tue, 6 Nov 2018 18:22:31 +0800 [thread overview]
Message-ID: <5eb42b84-5195-69f2-e7a7-97568f360506@huawei.com> (raw)
In-Reply-To: <20181106090642.GH22431@hirez.programming.kicks-ass.net>
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
>
>
next prev parent reply other threads:[~2018-11-06 10:22 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-13 6:47 [RFC PATCH] bit_spinlock: introduce smp_cond_load_relaxed Gao Xiang
2018-10-13 7:04 ` Greg Kroah-Hartman
2018-10-13 7:22 ` Gao Xiang
2018-10-13 7:30 ` Greg Kroah-Hartman
2018-10-13 7:44 ` Gao Xiang
2018-10-13 7:30 ` Gao Xiang
2018-10-30 6:04 ` [PATCH v2] " Gao Xiang
2018-10-30 5:52 ` Gao Xiang
2018-11-05 17:11 ` Gao Xiang
2018-11-05 22:49 ` Will Deacon
2018-11-06 1:45 ` Gao Xiang
2018-11-06 9:06 ` Peter Zijlstra
2018-11-06 10:22 ` Gao Xiang [this message]
2018-11-06 11:00 ` Peter Zijlstra
2018-11-06 11:36 ` Gao Xiang
2018-11-06 12:27 ` Peter Zijlstra
2018-11-06 12:33 ` Gao Xiang
2018-11-06 12:38 ` Gao Xiang
2018-11-06 12:43 ` Peter Zijlstra
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