87ed2b7f5a
The block cache implementation in loader has proven to be almost useless, and in worst case even slowing down the disk reads due to insufficient cache size and extra memory copy. Also the current cache implementation does not cache reads from CDs, or work with zfs built on top of multiple disks. Instead of an LRU, this code uses a simple hash (O(1) read from cache), and instead of a single global cache, a separate cache per block device. The cache also implements limited read-ahead to increase performance. To simplify read ahead management, the read ahead will not wrap over bcache end, so in worst case, single block physical read will be performed to fill the last block in bcache. Booting from a virtual CD over IPMI: 0ms latency, before: 27 second, after: 7 seconds 60ms latency, before: over 12 minutes, after: under 5 minutes. Submitted by: Toomas Soome <tsoome@me.com> Reviewed by: delphij (previous version), emaste (previous version) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D4713
128 lines
4.4 KiB
C
128 lines
4.4 KiB
C
/* $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 cgd Exp $ */
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/*-
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* Copyright (c) 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* The Mach Operating System project at Carnegie-Mellon University.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)read.c 8.1 (Berkeley) 6/11/93
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*
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*
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* Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
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* All Rights Reserved.
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*
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* Author: Alessandro Forin
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*
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* Permission to use, copy, modify and distribute this software and its
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* documentation is hereby granted, provided that both the copyright
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* notice and this permission notice appear in all copies of the
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* software, derivative works or modified versions, and any portions
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* thereof, and that both notices appear in supporting documentation.
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*
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* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
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* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
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* ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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*
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* Carnegie Mellon requests users of this software to return to
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*
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* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
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* School of Computer Science
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* Carnegie Mellon University
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* Pittsburgh PA 15213-3890
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*
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* any improvements or extensions that they make and grant Carnegie the
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* rights to redistribute these changes.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include "stand.h"
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ssize_t
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read(int fd, void *dest, size_t bcount)
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{
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struct open_file *f = &files[fd];
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size_t resid;
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if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
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errno = EBADF;
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return (-1);
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}
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if (f->f_flags & F_RAW) {
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twiddle(4);
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errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
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btodb(f->f_offset), 0, bcount, dest, &resid);
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if (errno)
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return (-1);
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f->f_offset += resid;
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return (resid);
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}
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/*
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* Optimise reads from regular files using a readahead buffer.
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* If the request can't be satisfied from the current buffer contents,
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* check to see if it should be bypassed, or refill the buffer and complete
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* the request.
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*/
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resid = bcount;
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for (;;) {
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size_t ccount, cresid;
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/* how much can we supply? */
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ccount = imin(f->f_ralen, resid);
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if (ccount > 0) {
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bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
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f->f_raoffset += ccount;
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f->f_ralen -= ccount;
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resid -= ccount;
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if (resid == 0)
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return(bcount);
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dest = (char *)dest + ccount;
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}
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/* will filling the readahead buffer again not help? */
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if (resid >= SOPEN_RASIZE) {
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/* bypass the rest of the request and leave the buffer empty */
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if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid)))
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return (-1);
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return(bcount - cresid);
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}
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/* fetch more data */
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if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
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return (-1);
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f->f_raoffset = 0;
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f->f_ralen = SOPEN_RASIZE - cresid;
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/* no more data, return what we had */
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if (f->f_ralen == 0)
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return(bcount - resid);
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}
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}
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