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fe5cbc6e06
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>
119 lines
2.8 KiB
Ucode
119 lines
2.8 KiB
Ucode
/* -*- linux-c -*- ------------------------------------------------------- *
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*
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* Copyright 2002-2004 H. Peter Anvin - All Rights Reserved
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, Inc., 53 Temple Place Ste 330,
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* Boston MA 02111-1307, USA; either version 2 of the License, or
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* (at your option) any later version; incorporated herein by reference.
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*
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* ----------------------------------------------------------------------- */
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/*
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* int$#.c
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*
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* $#-way unrolled portable integer math RAID-6 instruction set
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*
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* This file is postprocessed using unroll.awk
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*/
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#include <linux/raid/pq.h>
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/*
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* This is the C data type to use
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*/
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/* Change this from BITS_PER_LONG if there is something better... */
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#if BITS_PER_LONG == 64
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# define NBYTES(x) ((x) * 0x0101010101010101UL)
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# define NSIZE 8
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# define NSHIFT 3
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# define NSTRING "64"
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typedef u64 unative_t;
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#else
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# define NBYTES(x) ((x) * 0x01010101U)
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# define NSIZE 4
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# define NSHIFT 2
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# define NSTRING "32"
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typedef u32 unative_t;
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#endif
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/*
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* IA-64 wants insane amounts of unrolling. On other architectures that
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* is just a waste of space.
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*/
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#if ($# <= 8) || defined(__ia64__)
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/*
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* These sub-operations are separate inlines since they can sometimes be
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* specially optimized using architecture-specific hacks.
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*/
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/*
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* The SHLBYTE() operation shifts each byte left by 1, *not*
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* rolling over into the next byte
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*/
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static inline __attribute_const__ unative_t SHLBYTE(unative_t v)
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{
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unative_t vv;
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vv = (v << 1) & NBYTES(0xfe);
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return vv;
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}
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/*
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* The MASK() operation returns 0xFF in any byte for which the high
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* bit is 1, 0x00 for any byte for which the high bit is 0.
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*/
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static inline __attribute_const__ unative_t MASK(unative_t v)
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{
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unative_t vv;
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vv = v & NBYTES(0x80);
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vv = (vv << 1) - (vv >> 7); /* Overflow on the top bit is OK */
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return vv;
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}
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static void raid6_int$#_gen_syndrome(int disks, size_t bytes, void **ptrs)
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{
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u8 **dptr = (u8 **)ptrs;
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u8 *p, *q;
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int d, z, z0;
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unative_t wd$$, wq$$, wp$$, w1$$, w2$$;
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z0 = disks - 3; /* Highest data disk */
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p = dptr[z0+1]; /* XOR parity */
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q = dptr[z0+2]; /* RS syndrome */
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for ( d = 0 ; d < bytes ; d += NSIZE*$# ) {
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wq$$ = wp$$ = *(unative_t *)&dptr[z0][d+$$*NSIZE];
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for ( z = z0-1 ; z >= 0 ; z-- ) {
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wd$$ = *(unative_t *)&dptr[z][d+$$*NSIZE];
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wp$$ ^= wd$$;
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w2$$ = MASK(wq$$);
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w1$$ = SHLBYTE(wq$$);
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w2$$ &= NBYTES(0x1d);
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w1$$ ^= w2$$;
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wq$$ = w1$$ ^ wd$$;
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}
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*(unative_t *)&p[d+NSIZE*$$] = wp$$;
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*(unative_t *)&q[d+NSIZE*$$] = wq$$;
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}
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}
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const struct raid6_calls raid6_intx$# = {
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raid6_int$#_gen_syndrome,
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NULL, /* XOR not yet implemented */
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NULL, /* always valid */
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"int" NSTRING "x$#",
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0
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};
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#endif
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