linux/lib/raid6, branch v4.1

md/raid6 algorithms: xor_syndrome() for SSE2

2015-04-21T22:00:42Z

The second and (last) optimized XOR syndrome calculation. This version supports right and left side optimization. All CPUs with architecture older than Haswell will benefit from it. It should be noted that SSE2 movntdq kills performance for memory areas that are read and written simultaneously in chunks smaller than cache line size. So use movdqa instead for P/Q writes in sse21 and sse22 XOR functions. Signed-off-by: Markus Stockhausen Signed-off-by: NeilBrown

md/raid6 algorithms: xor_syndrome() for generic int

2015-04-21T22:00:42Z

Start the algorithms with the very basic one. It is left and right optimized. That means we can avoid all calculations for unneeded pages above the right stop offset. For pages below the left start offset we still need the syndrome multiplication but without reading data pages. Signed-off-by: Markus Stockhausen Signed-off-by: NeilBrown

md/raid6 algorithms: improve test program

2015-04-21T22:00:42Z

It is always helpful to have a test tool in place if we implement new data critical algorithms. So add some test routines to the raid6 checker that can prove if the new xor_syndrome() works as expected. Run through all permutations of start/stop pages per algorithm and simulate a xor_syndrome() assisted rmw run. After each rmw check if the recovery algorithm still confirms that the stripe is fine. Signed-off-by: Markus Stockhausen Signed-off-by: NeilBrown

md/raid6 algorithms: delta syndrome functions

2015-04-21T22:00:41Z

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 Signed-off-by: NeilBrown

x86/raid6: correctly check for assembler capabilities

2015-02-03T21:35:51Z

Just like for AVX2 (which simply needs an #if -> #ifdef conversion), SSSE3 assembler support should be checked for before using it. Signed-off-by: Jan Beulich Cc: Jim Kukunas Acked-by: Thomas Gleixner Signed-off-by: NeilBrown

lib/raid6: Add log level to printks

2014-10-14T02:08:29Z

Signed-off-by: Anton Blanchard Signed-off-by: NeilBrown

Merge tag 'md/3.12' of git://neil.brown.name/md

2013-09-10T20:03:41Z

Pull md update from Neil Brown: "Headline item is multithreading for RAID5 so that more IO/sec can be supported on fast (SSD) devices. Also TILE-Gx SIMD suppor for RAID6 calculations and an assortment of bug fixes" * tag 'md/3.12' of git://neil.brown.name/md: raid5: only wakeup necessary threads md/raid5: flush out all pending requests before proceeding with reshape. md/raid5: use seqcount to protect access to shape in make_request. raid5: sysfs entry to control worker thread number raid5: offload stripe handle to workqueue raid5: fix stripe release order raid5: make release_stripe lockless md: avoid deadlock when dirty buffers during md_stop. md: Don't test all of mddev->flags at once. md: Fix apparent cut-and-paste error in super_90_validate raid6/test: replace echo -e with printf RAID: add tilegx SIMD implementation of raid6 md: fix safe_mode buglet. md: don't call md_allow_write in get_bitmap_file.

raid6/test: replace echo -e with printf

2013-08-27T06:06:06Z

-e is a non-standard echo option, echo output is implementation-dependent when it is used. Replace echo -e with printf as suggested by POSIX echo manual. Cc: NeilBrown Cc: Jim Kukunas Cc: "H. Peter Anvin" Cc: Yuanhan Liu Acked-by: H. Peter Anvin Signed-off-by: Max Filippov Signed-off-by: NeilBrown

RAID: add tilegx SIMD implementation of raid6

2013-08-27T06:05:50Z

This change adds TILE-Gx SIMD instructions to the software raid (md), modeling the Altivec implementation. This is only for Syndrome generation; there is more that could be done to improve recovery, as in the recent Intel SSE3 recovery implementation. The code unrolls 8 times; this turns out to be the best on tilegx hardware among the set 1, 2, 4, 8 or 16. The code reads one cache-line of data from each disk, stores P and Q then goes to the next cache-line. The test code in sys/linux/lib/raid6/test reports 2008 MB/s data read rate for syndrome generation using 18 disks (16 data and 2 parity). It was 1512 MB/s before this SIMD optimizations. This is running on 1 core with all the data in cache. This is based on the paper The Mathematics of RAID-6. (http://kernel.org/pub/linux/kernel/people/hpa/raid6.pdf). Signed-off-by: Ken Steele Signed-off-by: Chris Metcalf Signed-off-by: NeilBrown

lib/raid6: add ARM-NEON accelerated syndrome calculation

2013-07-08T21:09:18Z

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 Acked-by: Nicolas Pitre Cc: hpa@linux.intel.com