{"id":54872,"date":"2020-01-06T00:00:00","date_gmt":"2020-01-05T21:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/blog_prohoster\/linus-torvalds-oproverg-problemy-s-planirovshhikom-zadach-vsplyvshie-v-teste-proizvoditelnosti"},"modified":"2020-02-18T14:02:55","modified_gmt":"2020-02-18T11:02:55","slug":"linus-torvalds-oproverg-problemy-s-planirovshhikom-zadach-vsplyvshie-v-teste-proizvoditelnosti","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/news\/linus-torvalds-oproverg-problemy-s-planirovshhikom-zadach-vsplyvshie-v-teste-proizvoditelnosti","title":{"rendered":"Linus Torvalds vyvr\u00e1til probl\u00e9my s pl\u00e1nova\u010dem \u00faloh, kter\u00e9 se objevily v testu v\u00fdkonu.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

V\u00fdvoj\u00e1\u0159 her Malte Skarupke vydal<\/a><\/noindex> srovn\u00e1n\u00ed v\u00fdkonnosti z\u00e1mk\u016f zalo\u017een\u00fdch na Mutex<\/a><\/noindex> a Spinlock<\/a><\/noindex> p\u0159i pou\u017e\u00edv\u00e1n\u00ed r\u016fzn\u00fdch pl\u00e1nova\u010d\u016f \u00faloh. Testy uk\u00e1zaly abnorm\u00e1ln\u011b velk\u00e9 zpo\u017ed\u011bn\u00ed p\u0159i pou\u017e\u00edv\u00e1n\u00ed Spinlock s pl\u00e1nova\u010dem \u00faloh pou\u017e\u00edvan\u00fdm ve v\u00fdchoz\u00edm nastaven\u00ed v Linuxu. Autor test\u016f dosp\u011bl k z\u00e1v\u011bru, \u017ee pl\u00e1nova\u010d \u00faloh v Linuxu m\u00e1 probl\u00e9my, kter\u00e9 negativn\u011b ovliv\u0148uj\u00ed v\u00fdkon her vyv\u00edjen\u00fdch pro slu\u017ebu Google Stadia, kde se hry vykon\u00e1vaj\u00ed na GPU v cloudov\u00e9m prost\u0159ed\u00ed a klientovi se pouze streamuje obsah obrazovky a\u017e p\u0159i 60 sn\u00edmc\u00edch za sekundu. V t\u011bchto podm\u00ednk\u00e1ch je nutn\u00e9 zajistit v\u010dasn\u00fd v\u00fdstup sn\u00edmk\u016f na obrazovku a zpo\u017ed\u011bn\u00ed p\u0159esahuj\u00edc\u00ed milisekundu jsou patrn\u00e1.<\/p>\n

K diskusi o testech se p\u0159ipojil<\/a><\/noindex> Linus Torvalds, kter\u00fd je nazval odpadem (\u00abpure garbage\u00bb) a p\u0159\u00edkladem toho, jak lze, ani\u017e byste se dostate\u010dn\u011b sezn\u00e1mili s t\u00e9matem, z\u00edskat hodnoty, kter\u00e9 neodr\u00e1\u017eej\u00ed skute\u010dnost. Spinlock je n\u00edzko\u00farov\u0148ov\u00fd primitiv, kter\u00fd je v u\u017eivatelsk\u00e9m prostoru t\u0159eba pou\u017e\u00edvat s velkou opatrnost\u00ed a pln\u00fdm porozum\u011bn\u00edm detail\u016fm, jinak m\u016f\u017eete z\u00edskat to, co autor testu p\u0159edvedl. Hr\u00e1\u010d\u016fm Linus doporu\u010dil, aby nepou\u017e\u00edvali spinlock a nepokou\u0161eli se vytv\u00e1\u0159et vlastn\u00ed syst\u00e9my z\u00e1mk\u016f na jeho z\u00e1klad\u011b, ale pou\u017e\u00edvali existuj\u00edc\u00ed osv\u011bd\u010den\u00e9 mechanismy, kter\u00e9 informuj\u00ed syst\u00e9m o \u010dek\u00e1n\u00ed na uvoln\u011bn\u00ed z\u00e1mku, aby se vylou\u010dil vliv pl\u00e1nova\u010de. <\/p>\n

Nadstavby na b\u00e1zi Spinlock lze pou\u017e\u00edvat pouze s plnou jistotou, \u017ee pl\u00e1nova\u010d jejich prov\u00e1d\u011bn\u00ed nep\u0159eru\u0161\u00ed. V testech pou\u017eit\u00e9 z\u00e1mky zalo\u017een\u00e9 na spinlocku jsou realizov\u00e1ny prost\u0159ednictv\u00edm dom\u00e1c\u00ed obalov\u00e9 funkce, pracuj\u00edc\u00ed v u\u017eivatelsk\u00e9m prostoru. Pl\u00e1nova\u010d \u00faloh m\u016f\u017ee kdykoli vy\u017e\u00e1dat \u0159\u00edzen\u00ed b\u011bhem prov\u00e1d\u011bn\u00ed t\u00e9to obalov\u00e9 funkce a p\u0159epnout na prov\u00e1d\u011bn\u00ed jin\u00e9 \u00falohy. Proto\u017ee m\u011b\u0159en\u00ed v\u00fdkonu je prov\u00e1d\u011bno na z\u00e1klad\u011b absolutn\u00edch hodnot \u010dasova\u010de, ur\u010dit\u00e9 v testech zpo\u017ed\u011bn\u00ed pokr\u00fdvaj\u00ed nejen zpo\u017ed\u011bn\u00ed zpracovatele z\u00e1mku, ale tak\u00e9 k\u00f3d, kter\u00fd byl proveden v jin\u00e9m kontextu, tj. m\u011b\u0159\u00ed nejen to, co se autor testu sna\u017eil zm\u011b\u0159it, ale tak\u00e9 \u201e\u0161um\u201c z ostatn\u00edch v\u00fdpo\u010dt\u016f v syst\u00e9mu.<\/p>\n

Autor testu se sna\u017eil<\/a><\/noindex> oponovat Linusu s t\u00edm, \u017ee pou\u017e\u00edv\u00e1n\u00ed vlastn\u00edch blokovac\u00edch syst\u00e9m\u016f zalo\u017een\u00fdch na spinlocku je v praxi \u010dasto pou\u017e\u00edv\u00e1no ve hr\u00e1ch, proto\u017ee p\u0159i pou\u017eit\u00ed jednodu\u0161\u0161\u00edch pl\u00e1nova\u010d\u016f ne\u017e v Linuxu ukazuj\u00ed testy vy\u0161\u0161\u00ed v\u00fdkon. Linus oponoval<\/a><\/noindex>, \u017ee pl\u00e1nova\u010d Linuxu je univerz\u00e1ln\u00ed, zdokonaloval se po desetilet\u00ed a je optimalizov\u00e1n nejen pro desktop a hry, ale i pro jin\u00e9 typy z\u00e1t\u011b\u017ee, jako jsou serverov\u00e9 syst\u00e9my, proto zohled\u0148uje mnoho nuanc\u00ed p\u0159i pl\u00e1nov\u00e1n\u00ed vykon\u00e1v\u00e1n\u00ed \u00faloh. <\/p>\n

P\u0159id\u00e1n\u00ed specifick\u00fdch optimalizac\u00ed, kter\u00e9 sn\u00ed\u017e\u00ed latenci ve hr\u00e1ch Google Stadia, m\u016f\u017ee zv\u00fd\u0161it citlivost v konkr\u00e9tn\u00edm p\u0159\u00edpad\u011b, ale pravd\u011bpodobn\u011b povede ke sn\u00ed\u017een\u00ed efektivity pl\u00e1nova\u010de jako celku. Nap\u0159\u00edklad pl\u00e1nova\u010d Windows se v diskutovan\u00fdch testech chov\u00e1 l\u00e9pe, proto\u017ee je v\u00fdrazn\u011b jednodu\u0161\u0161\u00ed ne\u017e pl\u00e1nova\u010d Linuxu a je optimalizov\u00e1n p\u0159ev\u00e1\u017en\u011b pro \u00fakoly specifick\u00e9 pro desktop.<\/p>\n

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

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

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