mirrors/linux-stable
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2024-09-21 10:01:00 +00:00
Code Issues Releases Wiki Activity
No description
1050165 commits 105 branches 5097 tags 5.5 GiB
C 97.6%
Assembly 1%
Shell 0.5%
Python 0.3%
Makefile 0.3%
Find a file
Thomas Richter e16b5f0779 perf stat: Fix forked applications enablement of counters 
[ Upstream commit d0a0a51149 ]

I have run into the following issue:

 # perf stat -a -e new_pmu/INSTRUCTION_7/ --  mytest -c1 7

 Performance counter stats for 'system wide':

                 0      new_pmu/INSTRUCTION_7/

       0.000366428 seconds time elapsed
 #

The new PMU for s390 counts the execution of certain CPU instructions.
The root cause is the extremely small run time of the mytest program. It
just executes some assembly instructions and then exits.

In above invocation the instruction is executed exactly one time (-c1
option). The PMU is expected to report this one time execution by a
counter value of one, but fails to do so in some cases, not all.

Debugging reveals the invocation of the child process is done
*before* the counter events are installed and enabled.

Tracing reveals that sometimes the child process starts and exits before
the event is installed on all CPUs. The more CPUs the machine has, the
more often this miscount happens.

Fix this by reversing the start of the work load after the events have
been installed on the specified CPUs. Now the comment also matches the
code.

Output after:

 # perf stat -a -e new_pmu/INSTRUCTION_7/ --  mytest -c1 7

 Performance counter stats for 'system wide':

                 1      new_pmu/INSTRUCTION_7/

       0.000366428 seconds time elapsed
 #

Now the correct result is reported rock solid all the time regardless
how many CPUs are online.

Reviewers notes:

Jiri:

Right, without -a the event has enable_on_exec so the race does not
matter, but it's a problem for system wide with fork.

Namhyung:

Agreed. Also we may move the enable_counters() and the clock code out of
the if block to be shared with the else block.

Fixes: acf2892270 ("perf stat: Use perf_evlist__prepare/start_workload()")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: https://lore.kernel.org/r/20220317155346.577384-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-04-08 14:23:51 +02:00
arch powerpc/pseries: Fix use after free in remove_phb_dynamic() 2022-04-08 14:23:42 +02:00
block block: don't delete queue kobject before its children 2022-04-08 14:23:07 +02:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto crypto: authenc - Fix sleep in atomic context in decrypt_tail 2022-04-08 14:23:05 +02:00
Documentation vsprintf: Fix %pK with kptr_restrict == 0 2022-04-08 14:23:18 +02:00
drivers driver core: dd: fix return value of __setup handler 2022-04-08 14:23:50 +02:00
fs NFSv4.1: don't retry BIND_CONN_TO_SESSION on session error 2022-04-08 14:23:51 +02:00
include serial: 8250: fix XOFF/XON sending when DMA is used 2022-04-08 14:23:50 +02:00
init init: make unknown command line param message clearer 2021-11-18 19:17:11 +01:00
ipc ipc/sem: do not sleep with a spin lock held 2022-02-08 18:34:03 +01:00
kernel kdb: Fix the putarea helper function 2022-04-08 14:23:51 +02:00
lib vsprintf: Fix %pK with kptr_restrict == 0 2022-04-08 14:23:18 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/kmemleak: reset tag when compare object pointer 2022-04-08 14:22:56 +02:00
net SUNRPC don't resend a task on an offlined transport 2022-04-08 14:23:51 +02:00
samples samples/bpf, xdpsock: Fix race when running for fix duration of time 2022-04-08 14:23:40 +02:00
scripts scripts/dtc: Call pkg-config POSIXly correct 2022-04-08 14:23:29 +02:00
security TOMOYO: fix __setup handlers return values 2022-04-08 14:23:35 +02:00
sound ASoC: amd: Fix reference to PCM buffer address 2022-04-08 14:23:22 +02:00
tools perf stat: Fix forked applications enablement of counters 2022-04-08 14:23:51 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Fix lockdep false negative during host resume 2022-03-16 14:23:40 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
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 MAINTAINERS: adjust file entry for of_net.c after movement 2022-03-08 19:12:53 +01:00
Makefile Linux 5.15.32 2022-03-28 09:58:46 +02:00
README

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.