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94 lines
3.7 KiB
C
94 lines
3.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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// Copyright (C) 2013 Andrea Mazzoleni
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#ifndef __RAID_MEMORY_H
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#define __RAID_MEMORY_H
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/**
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* Memory alignment provided by raid_malloc().
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*
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* It should guarantee good cache performance everywhere.
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*/
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#define RAID_MALLOC_ALIGN 256
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/**
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* Memory displacement to avoid cache address sharing on contiguous blocks,
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* used by raid_malloc_vector().
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*
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* When allocating a sequence of blocks with a size of power of 2,
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* there is the risk that the addresses of each block are mapped into the
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* same cache line and prefetching predictor, resulting in a lot of cache
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* sharing if you access all the blocks in parallel, from the start to the
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* end.
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*
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* To avoid this effect, it's better if all the blocks are allocated
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* with a fixed displacement trying to reduce the cache address sharing.
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*
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* The selected displacement was chosen empirically with some speed tests
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* with 8/12/16/20/24 data buffers of 256 KB.
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*
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* These are the results in MB/s with no displacement:
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*
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* RAID functions used for computing the parity with 'sync':
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* best int8 int32 int64 sse2 sse2e ssse3 ssse3e avx2 avx2e
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* gen1 avx2 14389 26472 42343 64085
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* gen2 avx2 3788 7309 20930 22042 36916
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* genz avx2e 2368 4262 11791 11786 21770
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* gen3 avx2e 809 11249 11913 21937
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* gen4 avx2e 609 8857 9469 17401
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* gen5 avx2e 488 7147 7465 14231
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* gen6 avx2e 398 5828 6381 12196
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*
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* These are the results with displacement of 9*256, resulting in improvements
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* in the order of 20% or more:
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*
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* RAID functions used for computing the parity with 'sync':
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* best int8 int32 int64 sse2 sse2e ssse3 ssse3e avx2 avx2e
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* gen1 avx2 18435 34980 62786 78159
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* gen2 avx2 5326 10026 26334 27349 45012
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* genz avx2e 3141 5037 14607 14099 25757
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* gen3 avx2e 1298 13289 14381 27563
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* gen4 avx2e 974 10076 11213 21637
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* gen5 avx2e 796 8091 8863 17458
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* gen6 avx2e 663 6761 7634 14912
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*/
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#define RAID_MALLOC_DISPLACEMENT (7*256)
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/**
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* Aligned malloc.
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* Use an alignment suitable for the raid functions.
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*/
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void *raid_malloc(size_t size, void **freeptr);
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/**
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* Arbitrary aligned malloc.
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*/
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void *raid_malloc_align(size_t size, size_t align_size, void **freeptr);
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/**
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* Aligned vector allocation.
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* Use an alignment suitable for the raid functions.
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* Returns a vector of @n pointers, each one pointing to a block of
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* the specified @size.
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* The first @nd elements are reversed in order.
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*/
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void **raid_malloc_vector(int nd, int n, size_t size, void **freeptr);
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/**
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* Arbitrary aligned vector allocation.
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*/
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void **raid_malloc_vector_align(int nd, int n, size_t size, size_t align_size, size_t displacement_size, void **freeptr);
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/**
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* Fills the memory vector with pseudo-random data based on the specified seed.
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*/
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void raid_mrand_vector(unsigned seed, int n, size_t size, void **vv);
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/**
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* Tests the memory vector for RAM problems.
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* If a problem is found, it crashes.
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*/
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int raid_mtest_vector(int n, size_t size, void **vv);
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#endif
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