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2a17a5bebc
Using mul_u64_u64_shr() provides similar calculation as mulhdu()
assembly function, but enables inlining by the compiler.
The home-made assembly function had special handling for when one of
the arguments is not a fully populated u64 but time functions use it
to multiply timebase by a calculated scale which is constructed to
have most significant bit set.
On mpc8xx sched_clock() runs 3% faster. On mpc83xx it is 2%.
As you can see below, sched_clock() is not much bigger than before:
c000cf68 <sched_clock>:
c000cf68: 7d 2d 42 a6 mftbu r9
c000cf6c: 7d 0c 42 a6 mftb r8
c000cf70: 7d 4d 42 a6 mftbu r10
c000cf74: 7c 09 50 40 cmplw r9,r10
c000cf78: 40 82 ff f0 bne c000cf68 <sched_clock>
c000cf7c: 3d 40 c1 37 lis r10,-16073
c000cf80: 38 8a b3 30 addi r4,r10,-19664
c000cf84: 80 ea b3 30 lwz r7,-19664(r10)
c000cf88: 80 64 00 14 lwz r3,20(r4)
c000cf8c: 39 40 00 00 li r10,0
c000cf90: 80 a4 00 04 lwz r5,4(r4)
c000cf94: 80 c4 00 10 lwz r6,16(r4)
c000cf98: 7c 63 40 10 subfc r3,r3,r8
c000cf9c: 80 84 00 08 lwz r4,8(r4)
c000cfa0: 7d 06 49 10 subfe r8,r6,r9
c000cfa4: 7c c7 19 d6 mullw r6,r7,r3
c000cfa8: 7d 25 18 16 mulhwu r9,r5,r3
c000cfac: 7c 08 29 d6 mullw r0,r8,r5
c000cfb0: 7c 67 18 16 mulhwu r3,r7,r3
c000cfb4: 7d 29 30 14 addc r9,r9,r6
c000cfb8: 7c a8 28 16 mulhwu r5,r8,r5
c000cfbc: 7c ca 51 14 adde r6,r10,r10
c000cfc0: 7d 67 41 d6 mullw r11,r7,r8
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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 reStructuredText 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.