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/* $LP: LPlib/source/LPdir_win.c,v 1.1 2004/06/14 10:07:56 _cvs_levitte Exp $ */
/*
 * Copyright (c) 2004, Richard Levitte <richard@levitte.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef LPDIR_H
#include "LPdir.h"
#endif

struct LP_dir_context_st { void *dummy; };
const char *LP_find_file(LP_DIR_CTX **ctx, const char *directory)
	{
	errno = EINVAL;
	return 0;
	}
int LP_find_file_end(LP_DIR_CTX **ctx)
	{
	errno = EINVAL;
	return 0;
	}
generated by cgit v1.2.3 (git 2.25.1) at 2024-08-21 23:29:06 +0000
g with 446216. If you look at /proc/diskstats, the eleven fields will be preceded by the major and minor device numbers, and device name. Each of these formats provides eleven fields of statistics, each meaning exactly the same things. All fields except field 9 are cumulative since boot. Field 9 should go to zero as I/Os complete; all others only increase (unless they overflow and wrap). Yes, these are (32-bit or 64-bit) unsigned long (native word size) numbers, and on a very busy or long-lived system they may wrap. Applications should be prepared to deal with that; unless your observations are measured in large numbers of minutes or hours, they should not wrap twice before you notice them. Each set of stats only applies to the indicated device; if you want system-wide stats you'll have to find all the devices and sum them all up. Field 1 -- # of reads completed This is the total number of reads completed successfully. Field 2 -- # of reads merged, field 6 -- # of writes merged Reads and writes which are adjacent to each other may be merged for efficiency. Thus two 4K reads may become one 8K read before it is ultimately handed to the disk, and so it will be counted (and queued) as only one I/O. This field lets you know how often this was done. Field 3 -- # of sectors read This is the total number of sectors read successfully. Field 4 -- # of milliseconds spent reading This is the total number of milliseconds spent by all reads (as measured from __make_request() to end_that_request_last()). Field 5 -- # of writes completed This is the total number of writes completed successfully. Field 6 -- # of writes merged See the description of field 2. Field 7 -- # of sectors written This is the total number of sectors written successfully. Field 8 -- # of milliseconds spent writing This is the total number of milliseconds spent by all writes (as measured from __make_request() to end_that_request_last()). Field 9 -- # of I/Os currently in progress The only field that should go to zero. Incremented as requests are given to appropriate struct request_queue and decremented as they finish. Field 10 -- # of milliseconds spent doing I/Os This field increases so long as field 9 is nonzero. Field 11 -- weighted # of milliseconds spent doing I/Os This field is incremented at each I/O start, I/O completion, I/O merge, or read of these stats by the number of I/Os in progress (field 9) times the number of milliseconds spent doing I/O since the last update of this field. This can provide an easy measure of both I/O completion time and the backlog that may be accumulating. To avoid introducing performance bottlenecks, no locks are held while modifying these counters. This implies that minor inaccuracies may be introduced when changes collide, so (for instance) adding up all the read I/Os issued per partition should equal those made to the disks ... but due to the lack of locking it may only be very close. In 2.6, there are counters for each CPU, which make the lack of locking almost a non-issue. When the statistics are read, the per-CPU counters are summed (possibly overflowing the unsigned long variable they are summed to) and the result given to the user. There is no convenient user interface for accessing the per-CPU counters themselves. Disks vs Partitions ------------------- There were significant changes between 2.4 and 2.6 in the I/O subsystem. As a result, some statistic information disappeared. The translation from a disk address relative to a partition to the disk address relative to the host disk happens much earlier. All merges and timings now happen at the disk level rather than at both the disk and partition level as in 2.4. Consequently, you'll see a different statistics output on 2.6 for partitions from that for disks. There are only *four* fields available for partitions on 2.6 machines. This is reflected in the examples above. Field 1 -- # of reads issued This is the total number of reads issued to this partition. Field 2 -- # of sectors read This is the total number of sectors requested to be read from this partition. Field 3 -- # of writes issued This is the total number of writes issued to this partition. Field 4 -- # of sectors written This is the total number of sectors requested to be written to this partition. Note that since the address is translated to a disk-relative one, and no record of the partition-relative address is kept, the subsequent success or failure of the read cannot be attributed to the partition. In other words, the number of reads for partitions is counted slightly before time of queuing for partitions, and at completion for whole disks. This is a subtle distinction that is probably uninteresting for most cases. More significant is the error induced by counting the numbers of reads/writes before merges for partitions and after for disks. Since a typical workload usually contains a lot of successive and adjacent requests, the number of reads/writes issued can be several times higher than the number of reads/writes completed. In 2.6.25, the full statistic set is again available for partitions and disk and partition statistics are consistent again. Since we still don't keep record of the partition-relative address, an operation is attributed to the partition which contains the first sector of the request after the eventual merges. As requests can be merged across partition, this could lead to some (probably insignificant) inaccuracy. Additional notes ---------------- In 2.6, sysfs is not mounted by default. If your distribution of Linux hasn't added it already, here's the line you'll want to add to your /etc/fstab: none /sys sysfs defaults 0 0 In 2.6, all disk statistics were removed from /proc/stat. In 2.4, they appear in both /proc/partitions and /proc/stat, although the ones in /proc/stat take a very different format from those in /proc/partitions (see proc(5), if your system has it.) -- ricklind@us.ibm.com
generated by cgit v1.2.3 (git 2.25.1) at 2024-08-21 23:29:06 +0000