linux-kernel - Re: [PATCH v3 2/5] locking/rwsem: Limit # of null owner retries for handoff writer

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Message-ID: <5d834f7a-dc62-308c-1017-1fb92c0efc62@redhat.com>
Date:   Tue, 25 Oct 2022 21:44:15 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org, john.p.donnelly@...cle.com,
        Hillf Danton <hdanton@...a.com>,
        Mukesh Ojha <quic_mojha@...cinc.com>,
        Ting11 Wang 王婷 <wangting11@...omi.com>
Subject: Re: [PATCH v3 2/5] locking/rwsem: Limit # of null owner retries for
 handoff writer

On 10/25/22 16:14, Peter Zijlstra wrote:
> On Tue, Oct 25, 2022 at 03:55:09PM -0400, Waiman Long wrote:
>
>> That is quite a number of changes spread over many different functions. That
>> is the kind of changes that may make it harder to backport to stable
>> releases.
> Yeah; don't care. it's the right thing to do. It also doesn't need to be
> reverted since it's a sane and good property for lock-ops to have.

I am sorry to confuse you. What I am saying is the original patch 2 of 
the series, not what you have proposed. I am fine about disabling 
preemption while running in the core rwsem code.

As a counter proposal, I will suggest modifying patch 2 to disable 
preemption for the reader rwsem code as the writer code already have 
preemption disabled in the most critical parts. Then I add another patch 
to complete the writer side conversion for symmetry. Are you OK with that?

Cheers,
Longman