linux-kernel - Re: [PATCH v2 1/2] Revert "locking/rwsem: Remove reader optimistic spinning"

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Message-ID: <20230904151008.GA25717@noisy.programming.kicks-ass.net>
Date:   Mon, 4 Sep 2023 17:10:08 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bongkyu Kim <bongkyu7.kim@...sung.com>
Cc:     mingo@...hat.com, will@...nel.org, longman@...hat.com,
        boqun.feng@...il.com, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH v2 1/2] Revert "locking/rwsem: Remove reader optimistic
 spinning"

On Fri, Sep 01, 2023 at 10:07:03AM +0900, Bongkyu Kim wrote:
> This reverts commit 617f3ef95177840c77f59c2aec1029d27d5547d6.
> 
> In mobile environment, reader optimistic spinning is still useful
> because there're not many readers. In my test result at android device,
> it improves application startup time about 3.8%
> App startup time is most important factor for android user expriences.
> So, re-enable reader optimistic spinning by this commit. And,
> the later patch will make it optional feature by cmdline.

I'm not seeing any mention on how this interacts with all the rwsem work
that has been done since that commit, like the handoff rework.

Why is a straight revert a sane thing at this point?