linux-kernel - Re: [PATCH-tip v7 00/20] locking/rwsem: Rwsem rearchitecture part 2

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Date:   Sun, 28 Apr 2019 19:19:08 -0400
From:   Waiman Long <longman@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH-tip v7 00/20] locking/rwsem: Rwsem rearchitecture part 2

On 4/28/19 7:12 PM, Waiman Long wrote:
> On 4/28/19 6:46 PM, Linus Torvalds wrote:
>> This doesn't seem to be the full diff - looking at that patch 1 you
>> seem to have taken my suggested list_cut_before() change too.
>>
>> I'm not against it (it does seem to be simpler and better), I just
>> hope you double-checked it, since I kind of hand-waved it.
>>
>>                     Linus
> I implemented your suggestion in patch 1 as it will produce simpler and
> faster code. However, one of the changes in my patchset is to wake up
> all the readers in the wait list. This means I have to jump over the
> writers and wake up the readers behind them as well. See patch 11 for
> details. As a result, I have to revert back to use list_add_tail() and
> list_for_each_entry_safe() for the first pass. That is why the diff for
> the whole patchset is just the below change. It is done on purpose, not
> an omission.

That is also the reason why it was implemented this way in my v6
patchset. I implemented the fix on top of the rwsem patchset first and
then move it backward to the beginning of the patchset for easier backport.

Cheers,
Longman