1 Организация подсистемы ввода-вывода CSS (Channel Subsystem) Лекция № 9

2 Channel Paths, Control Units, and Devices

3 Device Numbers Devices (such as disks, printers, screens) are assigned device numbers from 0 to 0xFFFF by the system administrator. These numbers are used in communication between a system operator and the operating system. These numbers do not need to be contiguous in a configuration.

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5 Subchannels The IOCP (I/O configuration program) reads the I/O configuration input deck. It defines the relationship between: – Channel paths – Control units and – Devices IOCP assign a subchannel number to each device. The numbers range from 0 to 0xFFFF and are contiguous.

6 Dynamic I/O Configuration The I/O configuration may be changed under software control by adding or deleting – Channel paths – Control units – Devices The software front-end is known as HCD (Hardware Configuration Definition)

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8 Изменения в подканалах (Modification of Subchannels) Часть блока SCHIB может быть изменена с помощью команды MODIFY SUBCHANNEL (MSCH), а именно: – подкласс прерывания I/O (ISC); – бит применения (E). MSCH обычно хранит блок SCHIB который использован (retrieved) перед командой START SUBCHANNEL (STSCH)

9 Starting an I/O operation

10 Starting an I/O operation

11 Operation-Request Block (ORB) The interruption parameter is saved by the channel subsystem and returned unchanged at the time of the I/O interrupt. It is normally used by the operating system to store the address of its own device control block. The logical path mask (LPM) can be used by the operating system to route an I/O operation to specific channel paths. Normally, the operating system sets this field to 0xFF to allow the channel subsystem to use any configured path. The channel program address points to the first channel command word (CCW).

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13 Типы кодов команд управляющего слова канала CCW CCW command code types: – Write (normal data output) – Read (normal data input) – Read backward (good for tapes) – Control (e.g. to position disk head) – Sense (retrieve reason for unit check) – Sense ID (retrieve device type, e.g. 3390) – Transfer in channel (branch in channel program) The particular command code is device-specific Коды операции CCW Код операции Выполняемые действия ~ ~ ~ ~ не используется m m m m m m 0 1записать m m m m m m 1 0прочитать m m m m прочитать в обратном направлении m m m m m m 1 1управление m m m m прочитать состояние прочитать уточненное состояние ~ ~ ~ ~ переход в канале (формат 0) переход в канале (формат 1) m m m m не используется m - биты модификации кодов в зависимости от типов устройств

14 CCW Flags CD: chain data (use the same CCW command on the next CCW) CC: chain command (0 = this is the last CCW) SLI: suppress incorrect length indication SKP: do not read data on input PCI: program-controlled interruption (generate intermediate I/O interrupt when this CCW is fetched) IDA: indirect data addressing S: suspend channel program without generating I/O interrupt

15 Indirect-Data-Address Words (IDAWs) IDAWs are used to describe I/O buffers that are contiguous in virtual storage – and thus usually scattered in absolute storage. – With z/Architecture, they provide the only means to address data buffers above 2G. IDAWs are used when the IDA flag is set in the CCW. The address in the CCW points to the list of IDAWs. – Format-1 IDAWs are 32 bits long and cover up to 2K of storage – Format-2 IDAWs are 64 bits long and cover up to 4K of storage When ORB word 1.14 (H) is 1, format-2 IDAWs are used. When ORB word 1.15 (T) is also 1, the IDAWs cover a 2K area, otherwise, they cover 4K.

16 Indirect-Data-Address Words (IDAWs)

17 Conclusion of I/O Operations When the last CCW has been processed, the channel signals ending status to the channel subsystem The subchannel is now made status-pending and an interruption condition is generated for its I/O-interruption subclass (ISC) An I/O interrupt is said to be floating, i.e. it is “offered” to all CPUs that are enabled for this ISC If more than one CPU is enabled for this I/O interrupt, only one will actually take it As an alternative, the CPU may poll for an interrupt using the TEST PENDING INTERRUPTION (TPI) instruction

18 Conclusion of I/O Operations

19 Conclusion of I/O Operations

20 Conclusion of I/O Operations

21 Conclusion of I/O Operations

22 Способы выполнения канальных программ В зависимости от типа каналов в z/Architecture возможны три способа выполнения канальных программ: –байт-мультиплексный (byte-multiplex mode); –блок-мультиплексный (burst mode); –фрейм-мультиплексный (frame-multiplex mode).

23 Структура фрейма

24 z990 Extensions to I/O Architecture Multiple channel subsystems (MCSS) 1 to 4 logical channel subsystems (LCSS) – Up to 256 channel paths per logical partition (LPAR) – Up to 63K devices (subchannels) per LPAR – An LCSS may be shared by multiple LPARs Allows much larger configurations (e.g. To consolidate two z900 systems on a single z990)

25 z990 – I/O Configuration Support

26 z990 – I/O Configuration Support

27 z9 Extensions to I/O Architecture Multiple subchannel sets (MSS) The problem: z990 had only one subchannel set – 64,512 subchannels (1,024 reserved for internal use) This became a problem for large installations because of PAV (parallel access volumes): – With PAV, a single disk drive often consumes four subchannels (base address plus three aliases) The solution z9 supports two subchannel sets – 65,280 subchannels in set 0 (256 reserved for internal use) – 65,535 subchannels in set 1 z/OS 1.7 exploits second subchannel set to access alias addresses of parallel access volumes (PAV)

28 z9 – I/O Configuration Growth - Multiple Subchannel Sets (MSS)

29 z9 – Multiple Subchannel Sets per LCSS

30 Modified Indirect-Data-Address Words (MIDAWs) MIDAWs were invented to increase I/O throughput by reducing the number of CCWs required. Like IDAWs, MIDAWs specify a list of data areas in absolute storage. Unlike IDAWs, MIDAWs are used to describe I/O buffers that are scattered in virtual storage: – MIDAWs never have to specify aligned addresses (the areas must not cross 4K-boundaries, though). – Each MIDAW has its own count field. MIDAWs were introduced with the IBM System z9. Use of MIDAWs must be enabled in the ORB (D-bit, word 1, bit 25). The MIDA flag must be set in the flags of the CCW (bit 15 in format- 1 CCW). When it is used, neither IDA nor SKIP flags must be set. The CCW points to a list of MIDAWs (MIDAL). The MIDAL begins on a quadword boundary. It must not cross a 4K boundary.

31 MIDAW layout

32 Initial Program Loading (IPL) Boots the operating system from an I/O device Initiated manually at the support element (SE) or hardware management console (HMC) System operator specifies device number Operator may specify an IPL parameter that is retrieved later by the operating system with a SERVICE CALL instruction (SERVC, also known as SCLP)

33 Initial Program Loading (IPL)

34 IPL Process

35 Функциональный состав CSS Настройка и управление ПУ Операции ввода- вывода виртуальные соединения между логическими разделами сервера Channel Subsystem – CSS канальные программы Channel Programs Внутренние каналы = подканалы Subchannels

36 Варианты исполнения CSS

37 Варианты исполнения CSS

38 Общая организация канальной подсистемы CSS

39 Параметры канальных подсистем S390 (G5/G6) z800, z900z990 CSS1 на сервер 2 на сервер Логические разделы 15 на сервер 15 на LCSS 30 на сервер Подканалы288 К на сервер 512 К на сервер 945 К на LCSS 1890 К на сервер Канальные пути 256 на CSS 256 на сервер 256 на сервер 256 на LCSS 256 на CSS 512 на сервер Периферий ные устройства 36 К на сервер 63 К на сервер 63 К на LCSS 126 К на сервер

40 Адресация в подсистеме ввода-вывода

41 Идентификация объектов канальной системы

42 Формат команды ввода-вывода Адресация устройств в командах ввода- вывода Команда ввода- вывода COPB2B2 D2D GR SCBNUM

43 Идентификация объектов канальной системы Идентификатор подсистемы ˜CSSIDIID0001SCBNUM

44 Принципы выполнения операций ввода- вывода в канальных подсистемах Распараллеливание работы большого числа периферийных устройств Каждой операции ввода-вывода Параллельно функционирующие каналы в CSS своя канальная программа, определяющая параметры обмена каналы реализуются как процессоры со специализированной системой команд

45 Принципы выполнения операций ввода-вывода в базовой архитектуре

46 Принципы выполнения операций ввода-вывода в базовой архитектуре

47 Выполнение операций ввода-вывода в архитектуре zSeries

48 Основные отличия канальной подсистемы z/Architecture от базовой архитектуры