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that works in the new threaded kernel. It was commented out of the disksort routine earlier this year for the reasons given in kern/subr_disklabel.c (which is where this code used to reside before it moved to kern/subr_disk.c): ---------------------------- revision 1.65 date: 2002/04/22 06:53:20; author: phk; state: Exp; lines: +5 -0 Comment out Kirks io-request priority hack until we can do this in a civilized way which doesn't cause grief. The problem is that it is not generally safe to cast a "struct bio *" to a "struct buf *". Things like ccd, vinum, ata-raid and GEOM constructs bio's which are not entrails of a struct buf. Also, curthread may or may not have anything to do with the I/O request at hand. The correct solution can either be to tag struct bio's with a priority derived from the requesting threads nice and have disksort act on this field, this wouldn't address the "silly-seek syndrome" where two equal processes bang the diskheads from one edge to the other of the disk repeatedly. Alternatively, and probably better: a sleep should be introduced either at the time the I/O is requested or at the time it is completed where we can be sure to sleep in the right thread. The sleep also needs to be in constant timeunits, 1/hz can be practicaly any sub-second size, at high HZ the current code practically doesn't do anything. ---------------------------- As suggested in this comment, it is no longer located in the disk sort routine, but rather now resides in spec_strategy where the disk operations are being queued by the thread that is associated with the process that is really requesting the I/O. At that point, the disk queues are not visible, so the I/O for positively niced processes is always slowed down whether or not there is other activity on the disk. On the issue of scaling HZ, I believe that the current scheme is better than using a fixed quantum of time. As machines and I/O subsystems get faster, the resolution on the clock also rises. So, ten years from now we will be slowing things down for shorter periods of time, but the proportional effect on the system will be about the same as it is today. So, I view this as a feature rather than a drawback. Hence this patch sticks with using HZ. Sponsored by: DARPA & NAI Labs. Reviewed by: Poul-Henning Kamp <phk@critter.freebsd.dk> |
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| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| kerberosIV | ||
| lib | ||
| libexec | ||
| release | ||
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| sys | ||
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| COPYRIGHT | ||
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| Makefile | ||
| Makefile.inc1 | ||
| Makefile.upgrade | ||
| README | ||
| UPDATING | ||
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you might need to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/<arch>/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/user commands. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc. games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberos5 Kerberos5 (Heimdal) package. kerberosIV KerberosIV (eBones) package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html