linux-kernel - Re: [PATCH v4 0/2] Fix how CPUs are enumerated when there's more than 255 CPUs

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Date:	Sat, 19 Sep 2015 00:38:40 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Lukasz Anaczkowski <lukasz.anaczkowski@...el.com>
Cc:	marc.zyngier@....com, lorenzo.pieralisi@....com,
	tomasz.nowicki@...aro.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, jason@...edaemon.net,
	len.brown@...el.com, pavel@....cz, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 0/2] Fix how CPUs are enumerated when there's more than 255 CPUs

On Wednesday, September 09, 2015 10:45:48 PM Rafael J. Wysocki wrote:
> On Wednesday, September 09, 2015 03:47:27 PM Lukasz Anaczkowski wrote:
> > This series of patches attempts to fix how CPUs are enumerated by kernel when
> > there's more than 255 of them on single processor.
> > In such case, BIOS may interleave APIC/X2APIC MADT subtables, to obey requirements
> > specified in ACPI spec. Without this patches, kernel then would first enumerate
> > BSP, then X2APIC then APIC, resulting in low APIC IDs to be assigned with high
> > logical IDs and high APIC IDs to be assigned low logical IDs. Biggest consequence
> > of that could be performance penalties due to wrong L2 cache sharing.
> > More details in patch 2/2.
> > 
> > Also, simpler approach has been considered, which did not required ACPI parsing
> > interface changes, however it failed to meet requirements. More details can be
> > found here: https://lkml.org/lkml/2015/9/7/285
> > 
> > Lukasz Anaczkowski (2):
> >   acpi: Added acpi_subtable_proc to ACPI table parsers
> >   x86, acpi: Handle apic/x2apic entries in MADT in correct order
> > 
> >  arch/x86/kernel/acpi/boot.c | 22 +++++++++--
> >  drivers/acpi/tables.c       | 91 ++++++++++++++++++++++++++++++++++++---------
> >  include/linux/acpi.h        | 19 ++++++++--
> >  3 files changed, 107 insertions(+), 25 deletions(-)
> 
> OK
> 
> Does anyone in the CC have any objections against merging this series?
> 
> If not, I'll queue it up as 4.3-rc material.

Well, I had a plan to push this for 4.3-rc2, but then I looked at it again
and realized that I'd like it to stay in linux-next for a couple of weeks
at least as I'm really unsure that it's not going to uncover some nastiness
somewhere.

Which practically means it's now scheduled for v4.4.

Thanks,
Rafael

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