linux-kernel - Re: [PATCH v1] rcu: Fix and improve RCU read lock checks when !CONFIG_DEBUG_LOCK

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Date:   Thu, 13 Jul 2023 12:59:27 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     paulmck@...nel.org
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Sandeep Dhavale <dhavale@...gle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        linux-erofs@...ts.ozlabs.org, xiang@...nel.org,
        Will Shiu <Will.Shiu@...iatek.com>, kernel-team@...roid.com,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v1] rcu: Fix and improve RCU read lock checks when
 !CONFIG_DEBUG_LOCK_ALLOC



On 2023/7/13 12:52, Paul E. McKenney wrote:
> On Thu, Jul 13, 2023 at 12:41:09PM +0800, Gao Xiang wrote:
>>
>>

...

>>
>> There are lots of performance issues here and even a plumber
>> topic last year to show that, see:
>>
>> [1] https://lore.kernel.org/r/20230519001709.2563-1-tj@kernel.org
>> [2] https://lore.kernel.org/r/CAHk-=wgE9kORADrDJ4nEsHHLirqPCZ1tGaEPAZejHdZ03qCOGg@mail.gmail.com
>> [3] https://lore.kernel.org/r/CAB=BE-SBtO6vcoyLNA9F-9VaN5R0t3o_Zn+FW8GbO6wyUqFneQ@mail.gmail.com
>> [4] https://lpc.events/event/16/contributions/1338/
>> and more.
>>
>> I'm not sure if it's necessary to look info all of that,
>> andSandeep knows more than I am (the scheduling issue
>> becomes vital on some aarch64 platform.)
> 
> Hmmm...  Please let me try again.
> 
> Assuming that this approach turns out to make sense, the resulting
> patch will need to clearly state the performance benefits directly in
> the commit log.
> 
> And of course, for the approach to make sense, it must avoid breaking
> the existing lockdep-RCU debugging code.
> 
> Is that more clear?

Personally I'm not working on Android platform any more so I don't
have a way to reproduce, hopefully Sandeep could give actually
number _again_ if dm-verity is enabled and trigger another
workqueue here and make a comparsion why the scheduling latency of
the extra work becomes unacceptable.

Thanks,
Gao Xiang