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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>
128 lines
3.3 KiB
Ucode
128 lines
3.3 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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* raid6altivec$#.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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* <benh> hpa: in process,
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* you can just "steal" the vec unit with enable_kernel_altivec() (but
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* bracked this with preempt_disable/enable or in a lock)
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*/
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#include <linux/raid/pq.h>
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#include <altivec.h>
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#ifdef __KERNEL__
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# include <asm/cputable.h>
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# include <asm/switch_to.h>
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/*
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* This is the C data type to use. We use a vector of
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* signed char so vec_cmpgt() will generate the right
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* instruction.
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*/
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typedef vector signed char unative_t;
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#define NBYTES(x) ((vector signed char) {x,x,x,x, x,x,x,x, x,x,x,x, x,x,x,x})
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#define NSIZE sizeof(unative_t)
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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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return vec_add(v,v);
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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 zv = NBYTES(0);
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/* vec_cmpgt returns a vector bool char; thus the need for the cast */
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return (unative_t)vec_cmpgt(zv, v);
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}
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/* This is noinline to make damned sure that gcc doesn't move any of the
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Altivec code around the enable/disable code */
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static void noinline
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raid6_altivec$#_gen_syndrome_real(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$$;
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unative_t x1d = NBYTES(0x1d);
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z0 = disks - 3; /* Highest data disk */
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p = dptr[z0+1]; /* XOR parity */
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q = dptr[z0+2]; /* RS syndrome */
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for ( d = 0 ; d < bytes ; d += NSIZE*$# ) {
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wq$$ = 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$$ = vec_xor(wp$$, wd$$);
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w2$$ = MASK(wq$$);
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w1$$ = SHLBYTE(wq$$);
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w2$$ = vec_and(w2$$, x1d);
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w1$$ = vec_xor(w1$$, w2$$);
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wq$$ = vec_xor(w1$$, 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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static void raid6_altivec$#_gen_syndrome(int disks, size_t bytes, void **ptrs)
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{
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preempt_disable();
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enable_kernel_altivec();
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raid6_altivec$#_gen_syndrome_real(disks, bytes, ptrs);
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preempt_enable();
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}
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int raid6_have_altivec(void);
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#if $# == 1
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int raid6_have_altivec(void)
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{
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/* This assumes either all CPUs have Altivec or none does */
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# ifdef __KERNEL__
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return cpu_has_feature(CPU_FTR_ALTIVEC);
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# else
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return 1;
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# endif
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}
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#endif
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const struct raid6_calls raid6_altivec$# = {
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raid6_altivec$#_gen_syndrome,
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NULL, /* XOR not yet implemented */
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raid6_have_altivec,
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"altivecx$#",
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0
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};
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#endif /* CONFIG_ALTIVEC */
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