linux-kernel - Re: [PATCH-tip 0/2] locking/rwsem: Rwsem rearchitecture part 2 follow-up patches

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Date:   Tue, 16 Apr 2019 15:49:07 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH-tip 0/2] locking/rwsem: Rwsem rearchitecture part 2
 follow-up patches

On 04/16/2019 01:37 PM, Peter Zijlstra wrote:
> On Tue, Apr 16, 2019 at 01:03:10PM -0400, Waiman Long wrote:
>> On 04/16/2019 10:17 AM, Peter Zijlstra wrote:
>>> On Tue, Apr 16, 2019 at 09:18:50AM -0400, Waiman Long wrote:
>>>> On 04/16/2019 09:10 AM, Peter Zijlstra wrote:
>>>>> On Mon, Apr 15, 2019 at 04:58:27PM -0400, Waiman Long wrote:
>>>>>> This series contain 2 follow-up patches to alleviate the performance
>>>>>> regression found in the page_fault1 test of the will-it-scale benchmark.
>>>>>> This does not recover all the lost performance, but reclaim a sizeable
>>>>>> portion of it.
>>>>>>
>>>>>> The regression was found on an Intel system. I have run the test on
>>>>>> an AMD system. The regression wasn't seen there.  There are only minor
>>>>>> variations in performance. Perhaps the page fault path is quite different
>>>>>> between Intel and AMD systems.
>>>>> Can you please just fold this back into the appropriate patches? Trying
>>>>> to review all the back and forth is painful.
>>>> I will send out an update part 2 patch with patch 1 of this series
>>>> merged into the writer spinning on reader patch. Patch 2 of this series
>>>> will be a standalone one.
>>> Hmm, in that case I can fold it back too. So hold off on sending it.
>>>
>>> I thought #2 was a fixup for an earlier patch as well.
>> #2 is a performance fix.
> Of this patch?
>
> 206038 N T Apr 13 Waiman Long     (7.5K) ├─>[PATCH v4 11/16] locking/rwsem: Enable readers spinning on writer
>
> Fixes should have a Fixes: tag. And if the patch it fixes isn't a commit
> yet, the patch should be refreshed to not need a fix.

The original patch isn't wrong. This patch just introduce another idea
to make it better. That is why I would still like to separate it as a
distinct patch.

Cheers,
Longman