LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
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


      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]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=e6f9465a-2d26-23c4-96b6-4c5945993e6d@redhat.com \
    --to=longman@redhat.com \
    --cc=bp@alien8.de \
    --cc=dave@stgolabs.net \
    --cc=hpa@zytor.com \
    --cc=huang.ying.caritas@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=tim.c.chen@linux.intel.com \
    --cc=torvalds@linux-foundation.org \
    --cc=will.deacon@arm.com \
    --cc=x86@kernel.org \
    --subject='Re: [PATCH] locking/lock_events: Use this_cpu_add() when necessary' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).