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Andy Shevchenko f599ae7529 rtc: cmos: Stop using shared IRQ 
commit b6da197a2e upstream.

As reported by Guilherme G. Piccoli:

---8<---8<---8<---

The rtc-cmos interrupt setting was changed in the commit 079062b28f
("rtc: cmos: prevent kernel warning on IRQ flags mismatch") in order
to allow shared interrupts; according to that commit's description,
some machine got kernel warnings due to the interrupt line being shared
between rtc-cmos and other hardware, and rtc-cmos didn't allow IRQ sharing
that time.

After the aforementioned commit though it was observed a huge increase
in lost HPET interrupts in some systems, observed through the following
kernel message:

[...] hpet1: lost 35 rtc interrupts

After investigation, it was narrowed down to the shared interrupts
usage when having the kernel option "irqpoll" enabled. In this case,
all IRQ handlers are called for non-timer interrupts, if such handlers
are setup in shared IRQ lines. The rtc-cmos IRQ handler could be set to
hpet_rtc_interrupt(), which will produce the kernel "lost interrupts"
message after doing work - lots of readl/writel to HPET registers, which
are known to be slow.

Although "irqpoll" is not a default kernel option, it's used in some contexts,
one being the kdump kernel (which is an already "impaired" kernel usually
running with 1 CPU available), so the performance burden could be considerable.
Also, the same issue would happen (in a shorter extent though) when using
"irqfixup" kernel option.

In a quick experiment, a virtual machine with uptime of 2 minutes produced
>300 calls to hpet_rtc_interrupt() when "irqpoll" was set, whereas without
sharing interrupts this number reduced to 1 interrupt. Machines with more
hardware than a VM should generate even more unnecessary HPET interrupts
in this scenario.

---8<---8<---8<---

After looking into the rtc-cmos driver history and DSDT table from
the Microsoft Surface 3, we may notice that Hans de Goede submitted
a correct fix (see dependency below). Thus, we simply revert
the culprit commit.

Fixes: 079062b28f ("rtc: cmos: prevent kernel warning on IRQ flags mismatch")
Depends-on: a1e23a42f1 ("rtc: cmos: Do not assume irq 8 for rtc when there are no legacy irqs")
Reported-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20200123131437.28157-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2020-02-14 16:34:12 -05:00
Documentation PM / devfreq: Add new name attribute for sysfs 2020-02-05 21:22:40 +00:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch x86/boot: Handle malformed SRAT tables during early ACPI parsing 2020-02-14 16:34:11 -05:00
block block: fix memleak of bio integrity data 2020-01-26 10:01:09 +01:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: api - Fix race condition in crypto_spawn_alg 2020-02-11 04:35:31 -08:00
drivers rtc: cmos: Stop using shared IRQ 2020-02-14 16:34:12 -05:00
fs NFSv4.0: nfs4_do_fsinfo() should not do implicit lease renewals 2020-02-14 16:34:11 -05:00
include RDMA/uverbs: Verify MR access flags 2020-02-14 16:34:08 -05:00
init Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:34:53 +00:00
ipc ipc/msg.c: consolidate all xxxctl_down() functions 2020-02-11 04:35:07 -08:00
kernel perf/core: Fix mlock accounting in perf_mmap() 2020-02-11 04:35:54 -08:00
lib lib/test_kasan.c: fix memory leak in kmalloc_oob_krealloc_more() 2020-02-11 04:35:14 -08:00
mm mm/mmu_gather: invalidate TLB correctly on batch allocation failure and flush 2020-02-11 04:35:42 -08:00
net bpf, sockmap: Check update requirements after locking 2020-02-14 16:34:10 -05:00
samples samples/bpf: Xdp_redirect_cpu fix missing tracepoint attach 2020-02-11 04:35:29 -08:00
scripts scripts/find-unused-docs: Fix massive false positives 2020-02-11 04:35:23 -08:00
security broken ping to ipv6 linklocal addresses on debian buster 2020-02-11 04:35:43 -08:00
sound ASoC: pcm: update FE/BE trigger order based on the command 2020-02-14 16:34:07 -05:00
tools selftests/bpf: Test freeing sockmap/sockhash with a socket in it 2020-02-14 16:34:09 -05:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-09 10:20:00 +01:00
virt KVM: Play nice with read-only memslots when querying host page size 2020-02-11 04:35:54 -08:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: correct entries for ISDN/mISDN section 2020-02-11 04:35:06 -08:00
Makefile Linux 5.4.19 2020-02-11 04:35:55 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.