Subversion Repositories HelenOS-doc

Rev

Rev 37 | Rev 39 | Go to most recent revision | Show entire file | Ignore whitespace | Details | Blame | Last modification | View Log | RSS feed

Rev 37 Rev 38
Line 16... Line 16...
16 
            </mediaobject>
 16 
            </mediaobject>
17 
        </para>
 17 
        </para>
18 
    </section>
 18 
    </section>
19 
 
 19 
 
20 
    <section>
 20 
    <section>
- 
 
 21 
        <title>Kernel primitives</title>
- 
 
 22 
        <para>
- 
 
 23 
        <termdef><glossterm>Thread</glossterm> is the basic execution primitive.</termdef>
- 
 
 24 
        </para>
- 
 
 25 
 
- 
 
 26 
        <para>
- 
 
 27 
        <termdef><glossterm>Thread context</glossterm> represents state of the <emphasis>thread</emphasis>.
- 
 
 28 
        Thread context is built of the context registers contents, FPU state and the stack.</termdef>
- 
 
 29 
        </para>
- 
 
 30 
 
- 
 
 31 
        <para>
- 
 
 32 
        <termdef>
- 
 
 33 
            <glossterm>Task</glossterm> is a multi-purpose entity, serving to
- 
 
 34 
            <itemizedlist>
- 
 
 35 
                <listitem>incorporate set if its threads</listitem>
- 
 
 36 
                <listitem>provide common address space to its threads</listitem>
- 
 
 37 
                <listitem>be an end-point in IPC</listitem>
- 
 
 38 
            </itemizedlist>
- 
 
 39 
 
- 
 
 40 
        </termdef>
- 
 
 41 
        </para>
- 
 
 42 
           
- 
 
 43 
        <para>
- 
 
 44 
        <termdef>
- 
 
 45 
            <glossterm>Address space area</glossterm> is a mutually disjunctive range of memory with the code, stack and data.
- 
 
 46 
        </termdef>
- 
 
 47 
        </para>
- 
 
 48 
 
- 
 
 49 
        <para>
- 
 
 50 
        <termdef>
- 
 
 51 
            <glossterm>Address space</glossterm> is a aggregating entity for address space areas, connecting them to the task.
- 
 
 52 
        </termdef>
- 
 
 53 
        </para>
- 
 
 54 
    </section>
- 
 
 55 
 
- 
 
 56 
    <section>
21 
        <title>Monolithic microkernel</title>
 57 
        <title>Monolithic microkernel</title>
22 
        <para>
 58 
        <para>
23 
            Though HelenOS was initially planned as a microkernel, we where trying to avoid several issues, connected
 59 
            Though HelenOS was initially planned as a microkernel, we were trying to avoid several issues, connected
24 
            with microkernels, such as much higher overhead during memory management and hardware operations. For this reason
 60 
            with microkernels, such as much higher overhead during memory management and hardware operations. For this reason
25 
            some of the subsytems, that are to be implmented as servers in classic microkernel design, where implemented
 61 
            some of the subsystems, that are to be implemented as servers in classic microkernel design, were implemented
26 
            as a part of kernel, thus minimizing this overhead.
 62 
            as a part of kernel, thus minimizing this overhead.
27 
        </para>
 63 
        </para>
28 
 
 64 
 
29 
        <formalpara>
 65 
        <formalpara>
30 
        <title>Memory management</title>
 66 
        <title>Memory management</title>
Line 52... Line 88...
52 
        </formalpara>
 88 
        </formalpara>
53 
 
 89 
 
54 
    </section>
 90 
    </section>
55 
 
 91 
 
56 
    <section>
 92 
    <section>
57 
        <title>Kernel primitives</title>
 - 
 
58 
        <para>
 - 
 
59 
        <termdef><glossterm>Thread</glossterm> is the basic execution primitive.</termdef>
 - 
 
60 
        </para>
 - 
 
61 
 
 - 
 
62 
        <para>
 - 
 
63 
        <termdef><glossterm>Thread context</glossterm> represents state of the <emphasis>thread</emphasis>. Contains registers state, FPU state, stack(s).</termdef>
 - 
 
64 
        </para>
 - 
 
65 
 
 - 
 
66 
        <para>
 - 
 
67 
        <termdef><glossterm>Task</glossterm> </termdef>
 - 
 
68 
        </para>
 - 
 
69 
 
 - 
 
70 
           
 - 
 
71 
        <para>
 - 
 
72 
        <termdef>
 - 
 
73 
            <glossterm>Address space area</glossterm> is a mutually disjunctive range of memory with the code, stack and data.
 - 
 
74 
        </termdef>
 - 
 
75 
        </para>
 - 
 
76 
 
 - 
 
77 
        <para>
 - 
 
78 
        <termdef>
 - 
 
79 
            <glossterm>Address space</glossterm> is a aggregating entity for address space areas, connecting them to the task.
 - 
 
80 
        </termdef>
 - 
 
81 
        </para>             1
 - 
 
82 
    </section>
 - 
 
83 
 
 - 
 
84 
 
 - 
 
85 
 
 - 
 
86 
    <section>
 - 
 
87 
        <title>IPC</title>
 93 
        <title>IPC</title>
88 
 
 94 
 
89 
        <para>
 - 
 
90 
            Due to the high intertask communication traffic, IPC becomes critical subsystem for microkernels, putting high demands on the
 - 
 
91 
            speed, latency and reliability of IPC model and implementation. HelenOS IPC is designed in analogy with telephone communication.
 95 
        <para>HelenOS IPC is designed in analogy with telephone communication.
92 
            Each task has an <emphasis>answerbox</emphasis> and a set of <emphasis>phones</emphasis> to call another tasks' answerboxes. Communication
 96 
            Each task has an <emphasis>answerbox</emphasis> and a set of <emphasis>phones</emphasis> to call another tasks' answerboxes.
- 
 
 97 
        </para>
- 
 
 98 
       
- 
 
 99 
        <para>Communication
93 
            is possible after the link establishment, and can be either <emphasis>asynchronious</emphasis> or <emphasis>synchronious</emphasis>.
 100 
            is possible after the connection is established, and can be either <emphasis>asynchronious</emphasis> or <emphasis>synchronious</emphasis>.
94 
         </para>
 101 
         </para>
95 
 
 102 
         
96 
    </section>
 103 
    </section>
97 
 
 104 
 
98 
 
 - 
 
99 
    <section>
 105 
    <section>
100 
        <para>Task ID - unique 64 bit number. Used for syscalls.</para>
 - 
 
101 
        <para>Contains threads</para>
 106 
        <title>Functionality model</title>
102 
        <para>Address space is created per task</para>
 - 
 
103 
        <para>Memory mapping is per task</para>
 - 
 
104 
        <para>Context per thread. (Note 2 stacks on IA64).</para>
 - 
 
105 
        <para>IPC answer box associated per task</para>
 - 
 
106 
 
 107 
 
107 
 
 - 
 
108 
        <title>Memory management</title>
 - 
 
109 
        <para>
 108 
        <para>
110 
        Zones - linked list (not many zones, so we can afford it. Can be replaced with B-tree in the future)
 109 
        As you know, microkernel design is very simple, just enough to provide communication facility for tasks. Most of the OS functionality
- 
 
 110 
        is performed by server tasks, that are running in userspace.
111 
        Number of zones depends on HW tables. Describe zone allocation/deallocation algoritm
 111 
        Thus most of the system calls in monolithic kernels, are the IPC calls on server tasks in microkernels.
112 
        </para>
 112 
        </para>
113 
        <para>Page tables. 4 level hierarchical and hash directly supported. B+ Tree can be implemented.</para>
 - 
 
114 
        <para>For paging there is an abstract layer</para>
 - 
 
115 
        <para>TLB shootdown implementation (update TLB upon mapping update/remove).
 - 
 
116 
        TLB shootdown ASID/ASID:PAGE/ALL.
 - 
 
117 
        TLB shootdown requests can come in asynchroniously
 - 
 
118 
        so there is a cache of TLB shootdown requests. Upon cache overflow TLB shootdown ALL is executed</para>
 - 
 
119 
       
 113 
       
120 
        <para>
 114 
        <para>
121 
            Address spaces. Address space area (B+ tree). Only for uspace. Set of syscalls (shrink/extend etc).
 115 
        Moreover, problems experience the device drivers. Running in the user space, device driver still needs to recieve interrupts
122 
            Special address space area type - device - prohibits shrink/extend syscalls to call on it.
 116 
        and access hardware directly.
123 
            Address space has link to mapping tables (hierarchical - per Address space, hash - global tables).
 - 
 
124 
        </para>
 117 
        </para>
- 
 
 118 
       
- 
 
 119 
        <para>
- 
 
 120 
        This raises two major problems in microkernels:
- 
 
 121 
       
- 
 
 122 
            <orderedlist numeration="loweralpha">
- 
 
 123 
            <listitem>What is the recipient address of the server (e.g. "memory manager" or a specific device driver) ?</listitem>
- 
 
 124 
            <listitem>How this server task is going to access hardware or kernel while running in the user mode?</listitem>
- 
 
 125 
            </orderedlist>
- 
 
 126 
           
- 
 
 127 
        </para>
- 
 
 128 
           
- 
 
 129 
       
- 
 
 130 
        <formalpara id="intro_ns">
- 
 
 131 
        <title>Name server</title>
- 
 
 132 
        <para>As every microkernel, HelenOS has a "Name server" task with "well known" IPC address, that connects user task to any server
- 
 
 133 
        just by the string service indentification.</para>
- 
 
 134 
        </formalpara>
- 
 
 135 
       
- 
 
 136 
       
- 
 
 137 
        <formalpara id="intro_ddi">
- 
 
 138 
        <title>Device driver interface</title>
- 
 
 139 
        <para>Device drivers use special syscalls to map physical memory areas into their address space, to map port regions (mostly ia32).
- 
 
 140 
        Interrupts are delivered to the device driver task by the standard IPC means.
- 
 
 141 
        </para>
- 
 
 142 
        </formalpara>
- 
 
 143 
       
125 
    </section>
 144 
    </section>
- 
 
 145 
 
- 
 
 146 
   
- 
 
 147 
   
- 
 
 148 
 
126 
</chapter>
 149 
</chapter>
127 
 
 150