1. 02 Nov, 2017 1 commit
    • Greg Kroah-Hartman's avatar
      License cleanup: add SPDX GPL-2.0 license identifier to files with no license · b2441318
      Greg Kroah-Hartman authored
      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
      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: default avatarKate Stewart <kstewart@linuxfoundation.org>
      Reviewed-by: default avatarPhilippe Ombredanne <pombredanne@nexb.com>
      Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
  2. 22 Jan, 2014 1 commit
    • Hannes Frederic Sowa's avatar
      reciprocal_divide: update/correction of the algorithm · 809fa972
      Hannes Frederic Sowa authored
      Jakub Zawadzki noticed that some divisions by reciprocal_divide()
      were not correct [1][2], which he could also show with BPF code
      after divisions are transformed into reciprocal_value() for runtime
      invariance which can be passed to reciprocal_divide() later on;
      reverse in BPF dump ended up with a different, off-by-one K in
      some situations.
      This has been fixed by Eric Dumazet in commit aee636c4
      ("bpf: do not use reciprocal divide"). This follow-up patch
      improves reciprocal_value() and reciprocal_divide() to work in
      all cases by using Granlund and Montgomery method, so that also
      future use is safe and without any non-obvious side-effects.
      Known problems with the old implementation were that division by 1
      always returned 0 and some off-by-ones when the dividend and divisor
      where very large. This seemed to not be problematic with its
      current users, as far as we can tell. Eric Dumazet checked for
      the slab usage, we cannot surely say so in the case of flex_array.
      Still, in order to fix that, we propose an extension from the
      original implementation from commit 6a2d7a95 resp. [3][4],
      by using the algorithm proposed in "Division by Invariant Integers
      Using Multiplication" [5], Torbjörn Granlund and Peter L.
      Montgomery, that is, pseudocode for q = n/d where q, n, d is in
      u32 universe:
      1) Initialization:
        int l = ceil(log_2 d)
        uword m' = floor((1<<32)*((1<<l)-d)/d)+1
        int sh_1 = min(l,1)
        int sh_2 = max(l-1,0)
      2) For q = n/d, all uword:
        uword t = (n*m')>>32
        q = (t+((n-t)>>sh_1))>>sh_2
      The assembler implementation from Agner Fog [6] also helped a lot
      while implementing. We have tested the implementation on x86_64,
      ppc64, i686, s390x; on x86_64/haswell we're still half the latency
      compared to normal divide.
      Joint work with Daniel Borkmann.
        [1] http://www.wireshark.org/~darkjames/reciprocal-buggy.c
        [2] http://www.wireshark.org/~darkjames/set-and-dump-filter-k-bug.c
        [3] https://gmplib.org/~tege/division-paper.pdf
        [4] http://homepage.cs.uiowa.edu/~jones/bcd/divide.html
        [5] http://citeseerx.ist.psu.edu/viewdoc/summary?doi=
        [6] http://www.agner.org/optimize/asmlib.zipReported-by: default avatarJakub Zawadzki <darkjames-ws@darkjames.pl>
      Cc: Eric Dumazet <eric.dumazet@gmail.com>
      Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
      Cc: linux-kernel@vger.kernel.org
      Cc: Jesse Gross <jesse@nicira.com>
      Cc: Jamal Hadi Salim <jhs@mojatatu.com>
      Cc: Stephen Hemminger <stephen@networkplumber.org>
      Cc: Matt Mackall <mpm@selenic.com>
      Cc: Pekka Enberg <penberg@kernel.org>
      Cc: Christoph Lameter <cl@linux-foundation.org>
      Cc: Andy Gospodarek <andy@greyhouse.net>
      Cc: Veaceslav Falico <vfalico@redhat.com>
      Cc: Jay Vosburgh <fubar@us.ibm.com>
      Cc: Jakub Zawadzki <darkjames-ws@darkjames.pl>
      Signed-off-by: default avatarDaniel Borkmann <dborkman@redhat.com>
      Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
  3. 09 Dec, 2011 1 commit
    • Eric Dumazet's avatar
      sch_red: Adaptative RED AQM · 8af2a218
      Eric Dumazet authored
      Adaptative RED AQM for linux, based on paper from Sally FLoyd,
      Ramakrishna Gummadi, and Scott Shenker, August 2001 :
      Goal of Adaptative RED is to make max_p a dynamic value between 1% and
      50% to reach the target average queue : (max_th - min_th) / 2
      Every 500 ms:
       if (avg > target and max_p <= 0.5)
        increase max_p : max_p += alpha;
       else if (avg < target and max_p >= 0.01)
        decrease max_p : max_p *= beta;
      target :[min_th + 0.4*(min_th - max_th),
                min_th + 0.6*(min_th - max_th)].
      alpha : min(0.01, max_p / 4)
      beta : 0.9
      max_P is a Q0.32 fixed point number (unsigned, with 32 bits mantissa)
      Changes against our RED implementation are :
      max_p is no longer a negative power of two (1/(2^Plog)), but a Q0.32
      fixed point number, to allow full range described in Adatative paper.
      To deliver a random number, we now use a reciprocal divide (thats really
      a multiply), but this operation is done once per marked/droped packet
      when in RED_BETWEEN_TRESH window, so added cost (compared to previous
      AND operation) is near zero.
      dump operation gives current max_p value in a new TCA_RED_MAX_P
      Example on a 10Mbit link :
      tc qdisc add dev $DEV parent 1:1 handle 10: est 1sec 8sec red \
         limit 400000 min 30000 max 90000 avpkt 1000 \
         burst 55 ecn adaptative bandwidth 10Mbit
      # tc -s -d qdisc show dev eth3
      qdisc red 10: parent 1:1 limit 400000b min 30000b max 90000b ecn
      adaptative ewma 5 max_p=0.113335 Scell_log 15
       Sent 50414282 bytes 34504 pkt (dropped 35, overlimits 1392 requeues 0)
       rate 9749Kbit 831pps backlog 72056b 16p requeues 0
        marked 1357 early 35 pdrop 0 other 0
      Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
  4. 13 Dec, 2006 1 commit
    • Eric Dumazet's avatar
      [PATCH] SLAB: use a multiply instead of a divide in obj_to_index() · 6a2d7a95
      Eric Dumazet authored
      When some objects are allocated by one CPU but freed by another CPU we can
      consume lot of cycles doing divides in obj_to_index().
      (Typical load on a dual processor machine where network interrupts are
      handled by one particular CPU (allocating skbufs), and the other CPU is
      running the application (consuming and freeing skbufs))
      Here on one production server (dual-core AMD Opteron 285), I noticed this
      divide took 1.20 % of CPU_CLK_UNHALTED events in kernel.  But Opteron are
      quite modern cpus and the divide is much more expensive on oldest
      architectures :
      On a 200 MHz sparcv9 machine, the division takes 64 cycles instead of 1
      cycle for a multiply.
      Doing some math, we can use a reciprocal multiplication instead of a divide.
      If we want to compute V = (A / B)  (A and B being u32 quantities)
      we can instead use :
      V = ((u64)A * RECIPROCAL(B)) >> 32 ;
      where RECIPROCAL(B) is precalculated to ((1LL << 32) + (B - 1)) / B
      Note :
      I wrote pure C code for clarity. gcc output for i386 is not optimal but
      acceptable :
      mull   0x14(%ebx)
      mov    %edx,%eax // part of the >> 32
      xor     %edx,%edx // useless
      mov    %eax,(%esp) // could be avoided
      mov    %edx,0x4(%esp) // useless
      mov    (%esp),%ebx
      [akpm@osdl.org: small cleanups]
      Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
      Cc: Christoph Lameter <clameter@sgi.com>
      Cc: David Miller <davem@davemloft.net>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>