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Steven Rostedt (VMware) 29ce24519c ring-buffer: Do not trigger a WARN if clock going backwards is detected
After tweaking the ring buffer to be a bit faster, a warning is triggering
on one of my machines, and causing my tests to fail. This warning is caused
when the delta (current time stamp minus previous time stamp), is larger
than the max time held by the ring buffer (59 bits).

If the clock were to go backwards slightly, this would then easily trigger
this warning. The machine that it triggered on, the clock did go backwards
by around 450 nanoseconds, and this happened after a recalibration of the
TSC clock. Now that the ring buffer is faster, it detects this, and the
delta that is used larger than the max, the warning is triggered and my test
fails.

To handle the clock going backwards, look at the saved before and after time
stamps. If they are the same, it means that the current event did not
interrupt another event, and that those timestamp are of a previous event
that was recorded. If the max delta is triggered, look at those time stamps,
make sure they are the same, then use them to compare with the current
timestamp. If the current timestamp is less than the before/after time
stamps, then that means the clock being used went backward.

Print out a message that this has happened, but do not warn about it (and
only print the message once).

Still do the warning if the delta is indeed larger than what can be used.

Also remove the unneeded KERN_WARNING from the WARN_ONCE() print.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
History 2020-07-01 22:12:07 -04:00
arch x86/ftrace: Do not jump to direct code in created trampolines 2020-06-29 11:42:48 -04:00
block block-5.8-2020-06-26 2020-06-27 08:59:32 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: drbg - always try to free Jitter RNG instance 2020-06-15 17:38:54 +10:00
Documentation Peter Zijlstra says: 2020-06-28 09:42:47 -07:00
drivers ARM: OMAP fixes for v5.8 2020-06-28 14:57:14 -07:00
fs - Fix build regression on v4.8 and older 2020-06-28 11:42:16 -07:00
include ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU 2020-06-30 17:18:56 -04:00
init Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
ipc mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
kernel ring-buffer: Do not trigger a WARN if clock going backwards is detected 2020-07-01 22:12:07 -04:00
lib Peter Zijlstra says: 2020-06-28 09:42:47 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm/memory_hotplug.c: fix false softlockup during pfn range removal 2020-06-26 00:27:38 -07:00
net NFS Client Bugfixes for Linux 5.8-rc 2020-06-27 09:35:47 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-06-25 18:27:40 -07:00
scripts Paul E. McKenney says: 2020-06-28 10:29:38 -07:00
security selinux/stable-5.8 PR 20200621 2020-06-21 15:41:24 -07:00
sound sound fixes for 5.8-rc3 2020-06-25 09:15:24 -07:00
tools Peter Zijlstra says: 2020-06-28 10:16:15 -07:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt MIPS: 2020-06-12 11:05:52 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: generate vmlinux.symvers and reuse it for the second modpost 2020-06-06 23:38:12 +09:00
.mailmap A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS ARM: SoC fixes for v5.8 2020-06-28 14:55:18 -07:00
Makefile Linux 5.8-rc3 2020-06-28 15:00:24 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.