{"id":90050,"date":"2020-07-28T13:42:44","date_gmt":"2020-07-28T11:42:44","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/google-nachal-otkrytie-realizaczii-modeli-potokov-mn"},"modified":"2020-07-28T13:42:44","modified_gmt":"2020-07-28T11:42:44","slug":"google-nachal-otkrytie-realizaczii-modeli-potokov-mn","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pt\/blog\/news\/google-nachal-otkrytie-realizaczii-modeli-potokov-mn","title":{"rendered":"O Google iniciou a implementa\u00e7\u00e3o do modelo de threads M:N","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

A empresa Google ofereceu<\/a><\/noindex> um conjunto inicial de patches para inclus\u00e3o no n\u00facleo Linux com a implementa\u00e7\u00e3o de componentes necess\u00e1rios para suportar o funcionamento do modelo de threads M:N. A iniciativa do Google est\u00e1 relacionada \u00e0 abertura de uma API que estava em desenvolvimento a portas fechadas SwitchTo<\/a><\/noindex> para o n\u00facleo Linux, que suporta a implementa\u00e7\u00e3o de um subsistema de m\u00faltiplas threads em espa\u00e7o de usu\u00e1rio, usando o modelo de threads M:N. O subsistema \u00e9 utilizado pelo Google para garantir o funcionamento de servi\u00e7os que requerem lat\u00eancias m\u00ednimas. O agendamento e o gerenciamento da distribui\u00e7\u00e3o de threads s\u00e3o feitos inteiramente no espa\u00e7o de usu\u00e1rio, o que permite reduzir significativamente o n\u00famero de opera\u00e7\u00f5es de troca de contexto ao minimizar as chamadas de sistema.<\/p>\n

Para garantir o funcionamento do subsistema especificado no n\u00edvel do n\u00facleo do Linux, foi implementada a API SwitchTo, que oferece tr\u00eas opera\u00e7\u00f5es b\u00e1sicas \u2014 wait, resume e swap (altern\u00e2ncia). Para inclus\u00e3o no n\u00facleo, foi proposto um c\u00f3digo para uma nova opera\u00e7\u00e3o FUTEX_SWAP, que complementa FUTEX_WAIT e FUTEX_WAKE<\/a><\/noindex>, e fornece uma base para a cria\u00e7\u00e3o de bibliotecas de m\u00faltiplas threads em espa\u00e7o de usu\u00e1rio. O FUTEX_SWAP tamb\u00e9m pode ser utilizado para a troca de mensagens entre tarefas, de forma semelhante ao RPC. Por exemplo, atualmente, para enviar uma mensagem entre tarefas, \u00e9 necess\u00e1rio realizar pelo menos quatro chamadas FUTEX_WAIT e FUTEX_WAKE, enquanto o uso do FUTEX_SWAP permitir\u00e1 uma opera\u00e7\u00e3o \u00fanica que ser\u00e1 executada de 5 a 10 vezes mais r\u00e1pido.<\/p>\n

\"O<\/a><\/noindex><\/center><\/p>\n

Atualmente, na pr\u00e1tica, s\u00e3o utilizadas principalmente os modelos de threads 1:1 e N:1. O modelo 1:1 \u00e9 usado em NPTL<\/a><\/noindex> (threads POSIX) e LinuxThreads<\/a><\/noindex>, e implica uma correspond\u00eancia direta de uma thread no espa\u00e7o de usu\u00e1rio com uma thread (unidade de agendamento) no n\u00edvel do n\u00facleo. O modelo N:1 \u00e9 implementado em GNU Pth<\/a><\/noindex>, deslocando a gest\u00e3o de threads para o espa\u00e7o de usu\u00e1rio e permitindo que N threads em espa\u00e7o de usu\u00e1rio fiquem ligadas a uma \u00fanica thread no n\u00facleo, sendo que o n\u00facleo n\u00e3o tem informa\u00e7\u00e3o sobre as threads de usu\u00e1rio.<\/p>\n

A principal desvantagem do modelo 1:1 s\u00e3o os altos custos de troca de contexto entre o n\u00facleo e o espa\u00e7o do usu\u00e1rio. O modelo N:1 resolve esse problema, mas cria um novo \u2014 como o thread no n\u00facleo \u00e9 uma unidade indivis\u00edvel de planejamento de execu\u00e7\u00e3o, os threads de usu\u00e1rio vinculados a uma thread no n\u00facleo do sistema operacional n\u00e3o podem ser escalonados entre os n\u00facleos da CPU e acabam ficando vinculados a um \u00fanico n\u00facleo da CPU.<\/p>\n

O modelo M:N \u00e9 h\u00edbrido e elimina todas as desvantagens descritas acima ao mapear N fluxos no espa\u00e7o do usu\u00e1rio para M fluxos no n\u00facleo do sistema operacional, o que permite reduzir o overhead da troca de contexto e garantir a escalabilidade entre os n\u00facleos da CPU. O pre\u00e7o dessa op\u00e7\u00e3o \u00e9 a complexidade adicional na implementa\u00e7\u00e3o do planejador de fluxos no espa\u00e7o do usu\u00e1rio e a necessidade de mecanismos de sincroniza\u00e7\u00e3o das a\u00e7\u00f5es com o planejador do n\u00facleo.<\/p>\n

\r\n \"Por\r\n
<\/div>\r\n <\/div><\/center><\/p>\n

<\/a><\/noindex><\/p>\n

Fonte: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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\u0440\u0430\u0437\u0432\u0438\u0432\u0430\u0432\u0448\u0435\u0433\u043e\u0441\u044f \u0437\u0430 \u0437\u0430\u043a\u0440\u044b\u0442\u044b\u043c\u0438 \u0434\u0432\u0435\u0440\u044f\u043c\u0438 API SwitchTo \u0434\u043b\u044f \u044f\u0434\u0440\u0430 Linux, \u043e\u0431\u0435\u0441\u043f\u0435\u0447\u0438\u0432\u0430\u044e\u0449\u0435\u0433\u043e \u0440\u0430\u0431\u043e\u0442\u0443 \u0440\u0435\u0430\u043b\u0438\u0437\u043e\u0432\u0430\u043d\u043d\u043e\u0439 \u0432 \u043f\u0440\u043e\u0441\u0442\u0440\u0430\u043d\u0441\u0442\u0432\u0435 \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u044f \u043c\u043d\u043e\u0433\u043e\u043f\u043e\u0442\u043e\u0447\u043d\u043e\u0439 \u043f\u043e\u0434\u0441\u0438\u0441\u0442\u0435\u043c\u044b, \u043f\u0440\u0438\u043c\u0435\u043d\u044f\u044e\u0449\u0435\u0439 \u043c\u043e\u0434\u0435\u043b\u044c \u043f\u043e\u0442\u043e\u043a\u043e\u0432 M:N. \u041f\u043e\u0434\u0441\u0438\u0441\u0442\u0435\u043c\u0430 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