xor.c

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/*
 * xor.c : Multiple Devices driver for Linux
 *
 * Copyright (C) 1996, 1997, 1998, 1999, 2000,
 * Ingo Molnar, Matti Aarnio, Jakub Jelinek, Richard Henderson.
 *
 * Dispatch optimized RAID-5 checksumming functions.
 *
 * 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; either version 2, or (at your option)
 * any later version.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#define BH_TRACE 0
#include <linux/module.h>
#include <linux/gfp.h>
#include <linux/raid/xor.h>
#include <linux/jiffies.h>
#include <linux/preempt.h>
#include <asm/xor.h>

/* The xor routines to use.  */
static struct xor_block_template *active_template;

void
xor_blocks(unsigned int src_count, unsigned int bytes, void *dest, void **srcs)
{
    unsigned long *p1, *p2, *p3, *p4;

    p1 = (unsigned long *) srcs[0];
    if (src_count == 1) {
        active_template->do_2(bytes, dest, p1);
        return;
    }

    p2 = (unsigned long *) srcs[1];
    if (src_count == 2) {
        active_template->do_3(bytes, dest, p1, p2);
        return;
    }

    p3 = (unsigned long *) srcs[2];
    if (src_count == 3) {
        active_template->do_4(bytes, dest, p1, p2, p3);
        return;
    }

    p4 = (unsigned long *) srcs[3];
    active_template->do_5(bytes, dest, p1, p2, p3, p4);
}
EXPORT_SYMBOL(xor_blocks);

/* Set of all registered templates.  */
static struct xor_block_template *__initdata template_list;

#define BENCH_SIZE (PAGE_SIZE)

static void __init
do_xor_speed(struct xor_block_template *tmpl, void *b1, void *b2)
{
    int speed;
    unsigned long now, j;
    int i, count, max;

    tmpl->next = template_list;
    template_list = tmpl;

    preempt_disable();

    /*
     * Count the number of XORs done during a whole jiffy, and use
     * this to calculate the speed of checksumming.  We use a 2-page
     * allocation to have guaranteed color L1-cache layout.
     */
    max = 0;
    for (i = 0; i < 5; i++) {
        j = jiffies;
        count = 0;
        while ((now = jiffies) == j)
            cpu_relax();
        while (time_before(jiffies, now + 1)) {
            mb(); /* prevent loop optimzation */
            tmpl->do_2(BENCH_SIZE, b1, b2);
            mb();
            count++;
            mb();
        }
        if (count > max)
            max = count;
    }

    preempt_enable();

    speed = max * (HZ * BENCH_SIZE / 1024);
    tmpl->speed = speed;

    printk(KERN_INFO "   %-10s: %5d.%03d MB/sec\n", tmpl->name,
           speed / 1000, speed % 1000);
}

static int __init
calibrate_xor_blocks(void)
{
    void *b1, *b2;
    struct xor_block_template *f, *fastest;

    /*
     * Note: Since the memory is not actually used for _anything_ but to
     * test the XOR speed, we don't really want kmemcheck to warn about
     * reading uninitialized bytes here.
     */
    b1 = (void *) __get_free_pages(GFP_KERNEL | __GFP_NOTRACK, 2);
    if (!b1) {
        printk(KERN_WARNING "xor: Yikes!  No memory available.\n");
        return -ENOMEM;
    }
    b2 = b1 + 2*PAGE_SIZE + BENCH_SIZE;

    /*
     * If this arch/cpu has a short-circuited selection, don't loop through
     * all the possible functions, just test the best one
     */

    fastest = NULL;

#ifdef XOR_SELECT_TEMPLATE
        fastest = XOR_SELECT_TEMPLATE(fastest);
#endif

#define xor_speed(templ)    do_xor_speed((templ), b1, b2)

    if (fastest) {
        printk(KERN_INFO "xor: automatically using best "
                 "checksumming function:\n");
        xor_speed(fastest);
        goto out;
    } else {
        printk(KERN_INFO "xor: measuring software checksum speed\n");
        XOR_TRY_TEMPLATES;
        fastest = template_list;
        for (f = fastest; f; f = f->next)
            if (f->speed > fastest->speed)
                fastest = f;
    }

    printk(KERN_INFO "xor: using function: %s (%d.%03d MB/sec)\n",
           fastest->name, fastest->speed / 1000, fastest->speed % 1000);

#undef xor_speed

 out:
    free_pages((unsigned long)b1, 2);

    active_template = fastest;
    return 0;
}

static __exit void xor_exit(void) { }

MODULE_LICENSE("GPL");

/* when built-in xor.o must initialize before drivers/md/md.o */
core_initcall(calibrate_xor_blocks);
module_exit(xor_exit);