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Our current int_sqrt() is not rough nor any approximation; it calculates
the exact value of: floor(sqrt()). Document this.
Link: http://lkml.kernel.org/r/20171020164645.001652117@infradead.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Anshul Garg <aksgarg1989@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: David Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Joe Perches <joe@perches.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Michael Davidson <md@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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The initial value (@m) compute is:
m = 1UL << (BITS_PER_LONG - 2);
while (m > x)
m >>= 2;
Which is a linear search for the highest even bit smaller or equal to @x
We can implement this using a binary search using __fls() (or better when
its hardware implemented).
m = 1UL << (__fls(x) & ~1UL);
Especially for small values of @x; which are the more common arguments
when doing a CDF on idle times; the linear search is near to worst case,
while the binary search of __fls() is a constant 6 (or 5 on 32bit)
branches.
cycles: branches: branch-misses:
PRE:
hot: 43.633557 +- 0.034373 45.333132 +- 0.002277 0.023529 +- 0.000681
cold: 207.438411 +- 0.125840 45.333132 +- 0.002277 6.976486 +- 0.004219
SOFTWARE FLS:
hot: 29.576176 +- 0.028850 26.666730 +- 0.004511 0.019463 +- 0.000663
cold: 165.947136 +- 0.188406 26.666746 +- 0.004511 6.133897 +- 0.004386
HARDWARE FLS:
hot: 24.720922 +- 0.025161 20.666784 +- 0.004509 0.020836 +- 0.000677
cold: 132.777197 +- 0.127471 20.666776 +- 0.004509 5.080285 +- 0.003874
Averages computed over all values <128k using a LFSR to generate order.
Cold numbers have a LFSR based branch trace buffer 'confuser' ran between
each int_sqrt() invocation.
Link: http://lkml.kernel.org/r/20171020164644.936577234@infradead.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: Joe Perches <joe@perches.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Anshul Garg <aksgarg1989@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: David Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Michael Davidson <md@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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The current int_sqrt() computation is sub-optimal for the case of small
@x. Which is the interesting case when we're going to do cumulative
distribution functions on idle times, which we assume to be a random
variable, where the target residency of the deepest idle state gives an
upper bound on the variable (5e6ns on recent Intel chips).
In the case of small @x, the compute loop:
while (m != 0) {
b = y + m;
y >>= 1;
if (x >= b) {
x -= b;
y += m;
}
m >>= 2;
}
can be reduced to:
while (m > x)
m >>= 2;
Because y==0, b==m and until x>=m y will remain 0.
And while this is computationally equivalent, it runs much faster
because there's less code, in particular less branches.
cycles: branches: branch-misses:
OLD:
hot: 45.109444 +- 0.044117 44.333392 +- 0.002254 0.018723 +- 0.000593
cold: 187.737379 +- 0.156678 44.333407 +- 0.002254 6.272844 +- 0.004305
PRE:
hot: 67.937492 +- 0.064124 66.999535 +- 0.000488 0.066720 +- 0.001113
cold: 232.004379 +- 0.332811 66.999527 +- 0.000488 6.914634 +- 0.006568
POST:
hot: 43.633557 +- 0.034373 45.333132 +- 0.002277 0.023529 +- 0.000681
cold: 207.438411 +- 0.125840 45.333132 +- 0.002277 6.976486 +- 0.004219
Averages computed over all values <128k using a LFSR to generate order.
Cold numbers have a LFSR based branch trace buffer 'confuser' ran between
each int_sqrt() invocation.
Link: http://lkml.kernel.org/r/20171020164644.876503355@infradead.org
Fixes: 30493cc9dddb ("lib/int_sqrt.c: optimize square root algorithm")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: Anshul Garg <aksgarg1989@gmail.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Joe Perches <joe@perches.com>
Cc: David Miller <davem@davemloft.net>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Michael Davidson <md@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.
By default all files without license information are under the default
license of the kernel, which is GPL version 2.
Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.
How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,
Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.
The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.
The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.
Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).
All documentation files were explicitly excluded.
The following heuristics were used to determine which SPDX license
identifiers to apply.
- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.
For non */uapi/* files that summary was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139
and resulted in the first patch in this series.
If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930
and resulted in the second patch in this series.
- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:
SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1
and that resulted in the third patch in this series.
- when the two scanners agreed on the detected license(s), that became
the concluded license(s).
- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.
- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).
- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.
- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.
In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.
Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.
Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.
In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.
Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct
This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.
These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Optimize the current version of the shift-and-subtract (hardware)
algorithm, described by John von Newmann[1] and Guy L Steele.
Iterating 1,000,000 times, perf shows for the current version:
Performance counter stats for './sqrt-curr' (10 runs):
27.170996 task-clock # 0.979 CPUs utilized ( +- 3.19% )
3 context-switches # 0.103 K/sec ( +- 4.76% )
0 cpu-migrations # 0.004 K/sec ( +-100.00% )
104 page-faults # 0.004 M/sec ( +- 0.16% )
64,921,199 cycles # 2.389 GHz ( +- 0.03% )
28,967,789 stalled-cycles-frontend # 44.62% frontend cycles idle ( +- 0.18% )
<not supported> stalled-cycles-backend
104,502,623 instructions # 1.61 insns per cycle
# 0.28 stalled cycles per insn ( +- 0.00% )
34,088,368 branches # 1254.587 M/sec ( +- 0.00% )
4,901 branch-misses # 0.01% of all branches ( +- 1.32% )
0.027763015 seconds time elapsed ( +- 3.22% )
And for the new version:
Performance counter stats for './sqrt-new' (10 runs):
0.496869 task-clock # 0.519 CPUs utilized ( +- 2.38% )
0 context-switches # 0.000 K/sec
0 cpu-migrations # 0.403 K/sec ( +-100.00% )
104 page-faults # 0.209 M/sec ( +- 0.15% )
590,760 cycles # 1.189 GHz ( +- 2.35% )
395,053 stalled-cycles-frontend # 66.87% frontend cycles idle ( +- 3.67% )
<not supported> stalled-cycles-backend
398,963 instructions # 0.68 insns per cycle
# 0.99 stalled cycles per insn ( +- 0.39% )
70,228 branches # 141.341 M/sec ( +- 0.36% )
3,364 branch-misses # 4.79% of all branches ( +- 5.45% )
0.000957440 seconds time elapsed ( +- 2.42% )
Furthermore, this saves space in instruction text:
text data bss dec hex filename
111 0 0 111 6f lib/int_sqrt-baseline.o
89 0 0 89 59 lib/int_sqrt.o
[1] http://en.wikipedia.org/wiki/First_Draft_of_a_Report_on_the_EDVAC
Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Reviewed-by: Jonathan Gonzalez <jgonzlez@linets.cl>
Tested-by: Jonathan Gonzalez <jgonzlez@linets.cl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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For files only using THIS_MODULE and/or EXPORT_SYMBOL, map
them onto including export.h -- or if the file isn't even
using those, then just delete the include. Fix up any implicit
include dependencies that were being masked by module.h along
the way.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
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The implementation of int_sqrt() assumes that longs have 32 bits. On
systems that have 64 bit longs this will result in gross errors when the
argument to the function is greater than 2^32 - 1 on such systems. I doubt
whether any such use is currently made of int_sqrt() but the attached patch
fixes the problem anyway.
Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
Cc: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
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