mirror of
https://github.com/torvalds/linux.git
synced 2024-11-16 09:02:00 +00:00
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>
129 lines
3.3 KiB
Ucode
129 lines
3.3 KiB
Ucode
/* -*- linux-c -*- ------------------------------------------------------- *
|
|
*
|
|
* Copyright 2002-2004 H. Peter Anvin - All Rights Reserved
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation, Inc., 53 Temple Place Ste 330,
|
|
* Boston MA 02111-1307, USA; either version 2 of the License, or
|
|
* (at your option) any later version; incorporated herein by reference.
|
|
*
|
|
* ----------------------------------------------------------------------- */
|
|
|
|
/*
|
|
* raid6altivec$#.c
|
|
*
|
|
* $#-way unrolled portable integer math RAID-6 instruction set
|
|
*
|
|
* This file is postprocessed using unroll.awk
|
|
*
|
|
* <benh> hpa: in process,
|
|
* you can just "steal" the vec unit with enable_kernel_altivec() (but
|
|
* bracked this with preempt_disable/enable or in a lock)
|
|
*/
|
|
|
|
#include <linux/raid/pq.h>
|
|
|
|
#include <altivec.h>
|
|
#ifdef __KERNEL__
|
|
# include <asm/cputable.h>
|
|
# include <asm/switch_to.h>
|
|
|
|
/*
|
|
* This is the C data type to use. We use a vector of
|
|
* signed char so vec_cmpgt() will generate the right
|
|
* instruction.
|
|
*/
|
|
|
|
typedef vector signed char unative_t;
|
|
|
|
#define NBYTES(x) ((vector signed char) {x,x,x,x, x,x,x,x, x,x,x,x, x,x,x,x})
|
|
#define NSIZE sizeof(unative_t)
|
|
|
|
/*
|
|
* The SHLBYTE() operation shifts each byte left by 1, *not*
|
|
* rolling over into the next byte
|
|
*/
|
|
static inline __attribute_const__ unative_t SHLBYTE(unative_t v)
|
|
{
|
|
return vec_add(v,v);
|
|
}
|
|
|
|
/*
|
|
* The MASK() operation returns 0xFF in any byte for which the high
|
|
* bit is 1, 0x00 for any byte for which the high bit is 0.
|
|
*/
|
|
static inline __attribute_const__ unative_t MASK(unative_t v)
|
|
{
|
|
unative_t zv = NBYTES(0);
|
|
|
|
/* vec_cmpgt returns a vector bool char; thus the need for the cast */
|
|
return (unative_t)vec_cmpgt(zv, v);
|
|
}
|
|
|
|
|
|
/* This is noinline to make damned sure that gcc doesn't move any of the
|
|
Altivec code around the enable/disable code */
|
|
static void noinline
|
|
raid6_altivec$#_gen_syndrome_real(int disks, size_t bytes, void **ptrs)
|
|
{
|
|
u8 **dptr = (u8 **)ptrs;
|
|
u8 *p, *q;
|
|
int d, z, z0;
|
|
|
|
unative_t wd$$, wq$$, wp$$, w1$$, w2$$;
|
|
unative_t x1d = NBYTES(0x1d);
|
|
|
|
z0 = disks - 3; /* Highest data disk */
|
|
p = dptr[z0+1]; /* XOR parity */
|
|
q = dptr[z0+2]; /* RS syndrome */
|
|
|
|
for ( d = 0 ; d < bytes ; d += NSIZE*$# ) {
|
|
wq$$ = wp$$ = *(unative_t *)&dptr[z0][d+$$*NSIZE];
|
|
for ( z = z0-1 ; z >= 0 ; z-- ) {
|
|
wd$$ = *(unative_t *)&dptr[z][d+$$*NSIZE];
|
|
wp$$ = vec_xor(wp$$, wd$$);
|
|
w2$$ = MASK(wq$$);
|
|
w1$$ = SHLBYTE(wq$$);
|
|
w2$$ = vec_and(w2$$, x1d);
|
|
w1$$ = vec_xor(w1$$, w2$$);
|
|
wq$$ = vec_xor(w1$$, wd$$);
|
|
}
|
|
*(unative_t *)&p[d+NSIZE*$$] = wp$$;
|
|
*(unative_t *)&q[d+NSIZE*$$] = wq$$;
|
|
}
|
|
}
|
|
|
|
static void raid6_altivec$#_gen_syndrome(int disks, size_t bytes, void **ptrs)
|
|
{
|
|
preempt_disable();
|
|
enable_kernel_altivec();
|
|
|
|
raid6_altivec$#_gen_syndrome_real(disks, bytes, ptrs);
|
|
|
|
preempt_enable();
|
|
}
|
|
|
|
int raid6_have_altivec(void);
|
|
#if $# == 1
|
|
int raid6_have_altivec(void)
|
|
{
|
|
/* This assumes either all CPUs have Altivec or none does */
|
|
# ifdef __KERNEL__
|
|
return cpu_has_feature(CPU_FTR_ALTIVEC);
|
|
# else
|
|
return 1;
|
|
# endif
|
|
}
|
|
#endif
|
|
|
|
const struct raid6_calls raid6_altivec$# = {
|
|
raid6_altivec$#_gen_syndrome,
|
|
NULL, /* XOR not yet implemented */
|
|
raid6_have_altivec,
|
|
"altivecx$#",
|
|
0
|
|
};
|
|
|
|
#endif /* CONFIG_ALTIVEC */
|