linux-kernel - Re: [RFT][PATCH v3 0/4] ACPI: ACPICA / OSL: Avoid unmapping ACPI memory inside of the AML interpreter

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Date:   Mon, 29 Jun 2020 13:46:03 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Erik Kaneda <erik.kaneda@...el.com>,
        Rafael J Wysocki <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Ira Weiny <ira.weiny@...el.com>,
        James Morse <james.morse@....com>,
        Myron Stowe <myron.stowe@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Bob Moore <robert.moore@...el.com>
Subject: Re: [RFT][PATCH v3 0/4] ACPI: ACPICA / OSL: Avoid unmapping ACPI
 memory inside of the AML interpreter

On Sun, Jun 28, 2020 at 10:09 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Fri, Jun 26, 2020 at 8:41 PM Dan Williams <dan.j.williams@...el.com> wrote:
> >
> > On Fri, Jun 26, 2020 at 10:34 AM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > >
> > > Hi All,
> > >
> > > On Monday, June 22, 2020 3:50:42 PM CEST Rafael J. Wysocki wrote:
> > > > Hi All,
> > > >
> > > > This series is to address the problem with RCU synchronization occurring,
> > > > possibly relatively often, inside of acpi_ex_system_memory_space_handler(),
> > > > when the namespace and interpreter mutexes are held.
> > > >
> > > > Like I said before, I had decided to change the approach used in the previous
> > > > iteration of this series and to allow the unmap operations carried out by
> > > > acpi_ex_system_memory_space_handler() to be deferred in the first place,
> > > > which is done in patches [1-2/4].
> > >
> > > In the meantime I realized that calling syncrhonize_rcu_expedited() under the
> > > "tables" mutex within ACPICA is not quite a good idea too and that there is no
> > > reason for any users of acpi_os_unmap_memory() in the tree to use the "sync"
> > > variant of unmapping.
> > >
> > > So, unless I'm missing something, acpi_os_unmap_memory() can be changed to
> > > always defer the final unmapping and the only ACPICA change needed to support
> > > that is the addition of the acpi_os_release_unused_mappings() call to get rid
> > > of the unused mappings when leaving the interpreter (module the extra call in
> > > the debug code for consistency).
> > >
> > > So patches [1-2/4] have been changed accordingly.
> > >
> > > > However, it turns out that the "fast-path" mapping is still useful on top of
> > > > the above to reduce the number of ioremap-iounmap cycles for the same address
> > > > range and so it is introduced by patches [3-4/4].
> > >
> > > Patches [3-4/4] still do what they did, but they have been simplified a bit
> > > after rebasing on top of the new [1-2/4].
> > >
> > > The below information is still valid, but it applies to the v3, of course.
> > >
> > > > For details, please refer to the patch changelogs.
> > > >
> > > > The series is available from the git branch at
> > > >
> > > >  git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git \
> > > >  acpica-osl
> > > >
> > > > for easier testing.
> > >
> > > Also the series have been tested locally.
> >
> > Ok, I'm still trying to get the original reporter to confirm this
> > reduces the execution time for ASL routines with a lot of OpRegion
> > touches. Shall I rebuild that test kernel with these changes, or are
> > the results from the original RFT still interesting?
>
> I'm mostly interested in the results with the v3 applied.
>

Ok, I just got feedback on v2 and it still showed the 30 minute
execution time where 7 minutes was achieved previously.

> Also it would be good to check the impact of the first two patches
> alone relative to all four.

I'll start with the full set and see if they can also support the
"first 2" experiment.