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Based on 2 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation #
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 4122 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Enrico Weigelt <info@metux.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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This implements XOR syndrome calculation using NEON intrinsics.
As before, the module can be built for ARM and arm64 from the
same source.
Relative performance on a Cortex-A57 based system:
raid6: int64x1 gen() 905 MB/s
raid6: int64x1 xor() 881 MB/s
raid6: int64x2 gen() 1343 MB/s
raid6: int64x2 xor() 1286 MB/s
raid6: int64x4 gen() 1896 MB/s
raid6: int64x4 xor() 1321 MB/s
raid6: int64x8 gen() 1773 MB/s
raid6: int64x8 xor() 1165 MB/s
raid6: neonx1 gen() 1834 MB/s
raid6: neonx1 xor() 1278 MB/s
raid6: neonx2 gen() 2528 MB/s
raid6: neonx2 xor() 1942 MB/s
raid6: neonx4 gen() 2888 MB/s
raid6: neonx4 xor() 2334 MB/s
raid6: neonx8 gen() 2957 MB/s
raid6: neonx8 xor() 2232 MB/s
raid6: using algorithm neonx8 gen() 2957 MB/s
raid6: .... xor() 2232 MB/s, rmw enabled
Cc: Markus Stockhausen <stockhausen@collogia.de>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NeilBrown <neilb@suse.com>
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v3: s-o-b comment, explanation of performance and descision for
the start/stop implementation
Implementing rmw functionality for RAID6 requires optimized syndrome
calculation. Up to now we can only generate a complete syndrome. The
target P/Q pages are always overwritten. With this patch we provide
a framework for inplace P/Q modification. In the first place simply
fill those functions with NULL values.
xor_syndrome() has two additional parameters: start & stop. These
will indicate the first and last page that are changing during a
rmw run. That makes it possible to avoid several unneccessary loops
and speed up calculation. The caller needs to implement the following
logic to make the functions work.
1) xor_syndrome(disks, start, stop, ...): "Remove" all data of source
blocks inside P/Q between (and including) start and end.
2) modify any block with start <= block <= stop
3) xor_syndrome(disks, start, stop, ...): "Reinsert" all data of
source blocks into P/Q between (and including) start and end.
Pages between start and stop that won't be changed should be filled
with a pointer to the kernel zero page. The reasons for not taking NULL
pages are:
1) Algorithms cross the whole source data line by line. Thus avoid
additional branches.
2) Having a NULL page avoids calculating the XOR P parity but still
need calulation steps for the Q parity. Depending on the algorithm
unrolling that might be only a difference of 2 instructions per loop.
The benchmark numbers of the gen_syndrome() functions are displayed in
the kernel log. Do the same for the xor_syndrome() functions. This
will help to analyze performance problems and give an rough estimate
how well the algorithm works. The choice of the fastest algorithm will
still depend on the gen_syndrome() performance.
With the start/stop page implementation the speed can vary a lot in real
life. E.g. a change of page 0 & page 15 on a stripe will be harder to
compute than the case where page 0 & page 1 are XOR candidates. To be not
to enthusiatic about the expected speeds we will run a worse case test
that simulates a change on the upper half of the stripe. So we do:
1) calculation of P/Q for the upper pages
2) continuation of Q for the lower (empty) pages
Signed-off-by: Markus Stockhausen <stockhausen@collogia.de>
Signed-off-by: NeilBrown <neilb@suse.de>
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Rebased/reworked a patch contributed by Rob Herring that uses
NEON intrinsics to perform the RAID-6 syndrome calculations.
It uses the existing unroll.awk code to generate several
unrolled versions of which the best performing one is selected
at boot time.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Cc: hpa@linux.intel.com
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