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Vincent Whitchurch 1beaef29c3 perf bench mem: Always memset source before memcpy
For memcpy, the source pages are memset to zero only when --cycles is
used.  This leads to wildly different results with or without --cycles,
since all sources pages are likely to be mapped to the same zero page
without explicit writes.

Before this fix:

$ export cmd="./perf stat -e LLC-loads -- ./perf bench \
  mem memcpy -s 1024MB -l 100 -f default"
$ $cmd

         2,935,826      LLC-loads
       3.821677452 seconds time elapsed

$ $cmd --cycles

       217,533,436      LLC-loads
       8.616725985 seconds time elapsed

After this fix:

$ $cmd

       214,459,686      LLC-loads
       8.674301124 seconds time elapsed

$ $cmd --cycles

       214,758,651      LLC-loads
       8.644480006 seconds time elapsed

Fixes: 47b5757bac ("perf bench mem: Move boilerplate memory allocation to the infrastructure")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel@axis.com
Link: http://lore.kernel.org/lkml/20200810133404.30829-1-vincent.whitchurch@axis.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2020-08-13 09:34:26 -03:00
Documentation zonefs changes for 5.9-rc1 2020-08-11 17:05:55 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch virtio: fixes, features 2020-08-11 14:34:17 -07:00
block A set of locking fixes and updates: 2020-08-10 19:07:44 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto mm, treewide: rename kzfree() to kfree_sensitive() 2020-08-07 11:33:22 -07:00
drivers chrome platform changes for 5.9 2020-08-11 17:28:32 -07:00
fs orangefs: a fix and a cleanup... 2020-08-11 17:08:11 -07:00
include chrome platform changes for 5.9 2020-08-11 17:28:32 -07:00
init A set of locking fixes and updates: 2020-08-10 19:07:44 -07:00
ipc mm: remove unnecessary wrapper function do_mmap_pgoff() 2020-08-07 11:33:27 -07:00
kernel libnvdimm for 5.9 2020-08-11 10:59:19 -07:00
lib Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
mm Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
net A set of locking fixes and updates: 2020-08-10 19:07:44 -07:00
samples Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
scripts Fix recordmcount build failure on non-arm64 (caused by an arm64 patch). 2020-08-11 14:43:12 -07:00
security Minor fixes for v5.9. 2020-08-11 14:30:36 -07:00
sound sound updates for 5.9 2020-08-06 14:27:31 -07:00
tools perf bench mem: Always memset source before memcpy 2020-08-13 09:34:26 -03:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt virtio: fixes, features 2020-08-11 14:34:17 -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 .gitignore: Add ZSTD-compressed files 2020-07-31 11:50:49 +02:00
.mailmap It's been a busy cycle for documentation - hopefully the busiest for a 2020-08-04 22:47:54 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Replace HTTP links with HTTPS ones 2020-07-23 14:53:58 -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 IOMMU Updates for Linux v5.9 2020-08-11 14:13:24 -07:00
Makefile Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
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.