freebsd kernel with SKQ
6fa8fbd029
g_io_deliver(). In such case it increases 'pace' counter on each ENOMEM and reschedules the request. The 'pace' counter is decreased for each request going down, but until 'pace' is greater than zero, GEOM will handle at most 10 requests per second. For GEOM GATE users that are proxy to local GEOM providers (like ggatel(8) and HAST) we can end up with almost permanent slow down of GEOM down queue. This is because once we reach GEOM GATE queue limit, we return ENOMEM to the GEOM. This means that we have, eg. 1024 I/O requests in the GEOM GATE queue. To make room in the queue and stop returning ENOMEM we need to proceed the requests of course, but those requests are handled by userland daemons that handle them by reading/writing also from/to local GEOM providers. For example with HAST, a new requests comes to /dev/hast/data, which is GEOM GATE provider. GEOM GATE passes the request to hastd(8) and hastd(8) reads/writes from/to /dev/da0. Once we reach GEOM GATE queue limit, to free up a slot in GEOM GATE queue, hastd(8) has to read/write from/to /dev/da0, but this request will also be very slow, because GEOM now slows down all the requests. We end up with full queue that we can unload at the speed of 10 requests per second. This simply looks like a deadlock. Fix it by allowing userland daemons that work with both GEOM GATE and local GEOM providers to specify unlimited queue size, so GEOM GATE will never return ENOMEM to the GEOM. MFC after: 1 week |
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| bin | ||
| cddl | ||
| contrib | ||
| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| Makefile.mips | ||
| ObsoleteFiles.inc | ||
| 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 ``world'' target should only be used in cases where the source tree has not changed from the currently running version. See: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html for more information, including setting make(1) variables. 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. cddl Various commands and libraries under the Common Development and Distribution License. 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. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. rescue Build system for statically linked /rescue utilities. 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