Brendan Gregg, \u00fcks DTrace arendajatest, kes n\u00fc\u00fcd arendab BPF-p\u00f5hiseid j\u00f5udluse anal\u00fc\u00fcsi vahendeid Linuxi tuumas, kogus kokku kogemused, mis saadi Netflixi probleemide anal\u00fc\u00fcsimisel, kui nad \u00fcletasid Cassandra andmebaasi CentOS-ist Ubuntu-sse Amazon EC2 pilvekeskkondades, mis on Xen-iga. P\u00e4rast migratsiooni suurenes CPU koormus 30% ja umbes sama palju suurenes kirjutamisoperatsioonide viivitus. Selgus, et rakenduste j\u00f5udlus, mis n\u00f5uavad ajainfot, s\u00f5ltub v\u00e4ga tugevalt s\u00fcsteemis valitud t\u00e4pse aja allikast. <\/p>\n
Alguses ei olnud j\u00f5udluse languse p\u00f5hjus ilmselge ning diagnoosimine algas v\u00f5imalike s\u00fcsteemsete protsesside pideva v\u00f5i perioodilise k\u00e4ivitamise m\u00f5ju j\u00e4lgimisega, kasutades utiliite top ja execsnoop. Kuid k\u00f5ik viitas sellele, et ressursitarbimine suurenes just Cassandra andmebaasis, mis on kirjutatud Java keeles. Kahe Cassandra protsessi, mis t\u00f6\u00f6tasid paralleelselt CentOS-is ja Ubuntu-s ning t\u00f6\u00f6tlesid samu p\u00e4ringuid, profiili v\u00f5rdlemine n\u00e4itas, et umbes 32% kogu ajast kulus os::javaTimeMillis() kutsumisele, mida kasutatakse praeguse aja teabe saamiseks. <\/p>\n
P\u00e4rast seda viidi l\u00e4bi katse, mille k\u00e4igus kirjutati lihtne rakendus Java keeles, mis kutsus meetodit System.currentTimeMillis() v\u00e4lja sada miljonit korda. Rakenduse k\u00e4ivitamine n\u00e4itas, et CentOS-is kulus selle t\u00e4itmiseks 13 sekundit, samas kui Ubuntu-s umbes 68 sekundit, st 5 korda aeglasem. Sarnane programm kirjutati C keeles, mis kutsus v\u00e4lja funktsiooni gettimeofday() sada miljonit korda, kuid selle k\u00e4igus saadi sarnased tulemused. <\/p>\n
Kuna sai selgeks, et probleemi allikaks on hetkeaja tagastamise funktsioon, suunati t\u00e4helepanu t\u00e4psete ajallikate valimise m\u00f5ju muutumisele s\u00fcsteemis. Datanurgade sisu p\u00f5hjal \"\/sys\/devices\/system\/clocksource\/clocksource0\/current_clocksource\" kasutas Linuxi k\u00e4ivitamisel vaikimisi ajutimerit \"xen\". Ajaallika muutmisel \"tsc\"-ks v\u00e4henes testrakenduse t\u00e4itmise aeg Ubuntu-s 68 sekundilt 3,3 sekundile, st muutus 20 korda kiiremaks. T\u00e4iendavalt viidi l\u00e4bi kvm-clock ajaallika j\u00f5udluse test, mille tulemused n\u00e4itasid, et viivitused suurenesid 20% v\u00f5rra v\u00f5rreldes TSC-iga. $ cat \/sys\/devices\/system\/clocksource\/clocksource0\/available_clocksource xen tsc hpet acpi_pm $ cat \/sys\/devices\/system\/clocksource\/clocksource0\/current_clocksource xen $ time java TimeBench real 1m8.300s user 0m38.337s sys 0m29.875s $ echo tsc > \/sys\/devices\/system\/clocksource\/clocksource0\/current_clocksource $ time java TimeBench real 0m3.370s user 0m3.353s sys 0m0.026s <\/p>\n
Aja saamiseks TSC allika valimisel kasutatakse protsessori k\u00e4sku RDTSC, mille t\u00e4itmine ei n\u00f5ua s\u00fcsteemi kutset (k\u00e4sk ei vaja k\u00f5rgendatud \u00f5igusi ja annab v\u00e4\u00e4rtuse CPU-sse sisse ehitatud ajakalkulaatorist). Vaikimisi ei aktiveerita TSC-d, kuna vanematel aegadel ei v\u00e4listanud see aja j\u00e4rjepidevat drifti, mida muudes t\u00f6\u00f6tlejates korrektiivselt programmeeritakse t\u00e4psemate n\u00e4itajate saavutamiseks. Inseneri arvates, kes on spetsialiseerunud protsessorite arendamisele, ei vasta mured aja nihkete \u00fcle TSC kasutamisel enam t\u00f5ele ja kaasaegsetel protsessoritel<\/a> see allikas v\u00f5ib aastaid anda stabiilseid n\u00e4itajaid. <\/p>\n T\u00f6\u00f6de t\u00f5lkimine serverid<\/a> Netflixis TSC-allika kasutamine t\u00f5i kaasa viivituste v\u00e4henemise 43% v\u00f5rra ja Ubuntu kasutamisel saavutati tulemused, mis \u00fcletasid CentOSi \"xen\" ajallikaga 4 korda. Teadusuuringute tulemused edastati ettev\u00f5ttele Amazon, mis soovitas ametlikult AWS EC2 Xen hypervisiordialustes keskkondades vaikimisi kasutada ajallikat TSC (Nitro hypervisori baasil keskkondades j\u00e4\u00e4b soovitatuks kvm-clock). \u0411\u0440\u0435\u043d\u0434\u0430\u043d \u0413\u0440\u0435\u0433 (Brendan Gregg), \u043e\u0434\u0438\u043d \u0438\u0437 \u0440\u0430\u0437\u0440\u0430\u0431\u043e\u0442\u0447\u0438\u043a\u043e\u0432 DTrace, \u043d\u044b\u043d\u0435 \u0440\u0430\u0437\u0432\u0438\u0432\u0430\u044e\u0449\u0438\u0439 \u0441\u0440\u0435\u0434\u0441\u0442\u0432\u0430 \u0434\u043b\u044f \u0430\u043d\u0430\u043b\u0438\u0437\u0430 \u043f\u0440\u043e\u0438\u0437\u0432\u043e\u0434\u0438\u0442\u0435\u043b\u044c\u043d\u043e\u0441\u0442\u0438 \u043d\u0430 \u0431\u0430\u0437\u0435 BPF \u0432 \u044f\u0434\u0440\u0435 Linux, \u043e\u0431\u043e\u0431\u0449\u0438\u043b \u043e\u043f\u044b\u0442, \u043f\u043e\u043b\u0443\u0447\u0435\u043d\u043d\u044b\u0439 \u0432 \u0445\u043e\u0434\u0435 \u0440\u0430\u0437\u0431\u043e\u0440\u0430 \u043f\u0440\u043e\u0431\u043b\u0435\u043c \u0441 \u043f\u0440\u043e\u0438\u0437\u0432\u043e\u0434\u0438\u0442\u0435\u043b\u044c\u043d\u043e\u0441\u0442\u044c\u044e, \u0441 \u043a\u043e\u0442\u043e\u0440\u044b\u043c\u0438 \u043a\u043e\u043c\u043f\u0430\u043d\u0438\u044f Netflix \u0441\u0442\u043e\u043b\u043a\u043d\u0443\u043b\u0430\u0441\u044c \u043f\u0440\u0438 \u043f\u0435\u0440\u0435\u0432\u043e\u0434\u0435 \u0421\u0423\u0411\u0414 Cassandra c CentOS \u043d\u0430 Ubuntu \u0432 \u043e\u043a\u0440\u0443\u0436\u0435\u043d\u0438\u044f\u0445, \u0432\u044b\u043f\u043e\u043b\u043d\u044f\u0435\u043c\u044b\u0445 \u0432 \u043e\u0431\u043b\u0430\u043a\u0435 Amazon EC2 \u043d\u0430 \u0431\u0430\u0437\u0435 Xen. \u041f\u043e\u0441\u043b\u0435 \u043c\u0438\u0433\u0440\u0430\u0446\u0438\u0438 \u043d\u0430\u0433\u0440\u0443\u0437\u043a\u0430 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-101444","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Valitud s\u00fcsteemi ajaallika j\u00f5udlusele m\u00f5ju anal\u00fc\u00fcs | ProHoster","description":"Brendan Gregg, \u00fcks DTrace'i arendajatest, kes praegu arendab BPF-p\u00f5hiseid t\u00f6\u00f6riistu j\u00f5udluse anal\u00fc\u00fcsimiseks Linuxi kernelis, on kokku v\u00f5tnud kogemuse, mis on saadud j\u00f5udlusprobleemide lahendamise 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Allikas: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"