Re: [6.1] Please apply cc6003916ed46d7a67d91ee32de0f9138047d55f

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Oct 20, 2023 at 11:46:36AM +0900, Hyeonggon Yoo wrote:
> On Fri, Oct 20, 2023 at 10:27 AM Luiz Capitulino <luizcap@amazon.com> wrote:
> >
> > Hi,
> >
> > As reported before[1], we found another regression in 6.1 when doing
> > performance comparisons with 5.10. This one is caused by CONFIG_DEBUG_PREEMPT
> > being enabled by default by the following upstream commit if you have the
> > right config dependencies enabled (commit is introduced in v5.16-rc1):
> >
> > """
> > commit c597bfddc9e9e8a63817252b67c3ca0e544ace26
> > Author: Frederic Weisbecker <frederic@kernel.org>
> > Date: Tue Sep 14 12:31:34 2021 +0200
> >
> > sched: Provide Kconfig support for default dynamic preempt mode
> > """
> >
> > We found up to 8% performance improvement with CONFIG_DEBUG_PREEMPT
> > disabled in different perf benchmarks (including UnixBench process
> > creation and redis). The root cause is explained in the commit log
> > below which is merged in 6.3 and applies (almost) clealy on 6.1.59.
> 
> Oh, I should've sent it to the stable. Thanks for sending it!
> 
> Yes, DEBUG_PREEMPT was unintentionally enabled after the introduction
> of PREEMPT_DYNAMIC. It was already enabled by default for PREEMPTION=y kernels
> but PREEMPT_DYNAMIC always enables PREEMPT_BUILD (and hence PREEMPTION)
> so distros that were using PREEMPT_VOLUNTARY are silently affected by that.
> 
> It looks appropriate to be backported to the stable tree (to me).
> Hmm but I think it should be backported to 5.15 too?

Now queued up, thanks.

greg k-h