From: Waiman Long <longman@redhat.com>
To: Will Deacon <will.deacon@arm.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Tim Chen <tim.c.chen@linux.intel.com>,
huang ying <huang.ying.caritas@gmail.com>
Subject: Re: [PATCH] locking/lock_events: Use this_cpu_add() when necessary
Date: Fri, 24 May 2019 13:00:14 -0400 [thread overview]
Message-ID: <e6f9465a-2d26-23c4-96b6-4c5945993e6d@redhat.com> (raw)
In-Reply-To: <20190523145839.GB31896@fuggles.cambridge.arm.com>
On 5/23/19 10:58 AM, Will Deacon wrote:
> On Wed, May 22, 2019 at 12:54:13PM -0700, Linus Torvalds wrote:
>> On Wed, May 22, 2019 at 8:40 AM Waiman Long <longman@redhat.com> wrote:
>>> +#if defined(CONFIG_PREEMPT) && \
>>> + (defined(CONFIG_DEBUG_PREEMPT) || !defined(CONFIG_X86))
>>> +#define lockevent_percpu_inc(x) this_cpu_inc(x)
>>> +#define lockevent_percpu_add(x, v) this_cpu_add(x, v)
>> Why that CONFIG_X86 special case?
>>
>> On x86, the regular non-underscore versionm is perfectly fine, and the
>> underscore is no faster or simpler.
>>
>> So just make it be
>>
>> #if defined(CONFIG_PREEMPT)
>> .. non-underscore versions..
>> #else
>> .. underscore versions ..
>> #endif
>>
>> and realize that x86 simply doesn't _care_. On x86, it will be one
>> single instruction regardless.
>>
>> Non-x86 may prefer the underscore versions for the non-preempt case.
> To be honest, given this depends on LOCK_EVENT_COUNTS, I'd be inclined to
> keep things simple and drop the underscore versions entirely. Saves having
> to worry about things like "could I take an interrupt during the add?".
>
I have sent out the v2 patch that simplifies the condition. Now the
underscore versions will be used for !preempt kernel and non-underscore
version used in preempt kernel. The non-underscore versions may generate
a lot more unnecessary code when CONFIG_PREEMPT_COUNT is defined.
Cheers,
Longman
prev parent reply other threads:[~2019-05-24 17:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-22 15:39 Waiman Long
2019-05-22 19:54 ` Linus Torvalds
2019-05-22 20:50 ` Waiman Long
2019-05-23 14:58 ` Will Deacon
2019-05-24 17:00 ` Waiman Long [this message]
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