Re: [PATCH v1] rcu: Fix and improve RCU read lock checks when !CONFIG_DEBUG_LOCK_ALLOC

[Gao Xiang]

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@xxxxxxxxxx
> > [2] https://lore.kernel.org/r/CAHk-=wgE9kORADrDJ4nEsHHLirqPCZ1tGaEPAZejHdZ03qCOGg@xxxxxxxxxxxxxx
> > [3] https://lore.kernel.org/r/CAB=BE-SBtO6vcoyLNA9F-9VaN5R0t3o_Zn+FW8GbO6wyUqFneQ@xxxxxxxxxxxxxx
> > [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