Brendan Gregg, jeden z v\u00fdvoj\u00e1\u0159\u016f DTrace, kter\u00fd nyn\u00ed vyv\u00edj\u00ed n\u00e1stroje pro anal\u00fdzu v\u00fdkonu zalo\u017een\u00e9 na BPF v j\u00e1d\u0159e Linux, shrnul zku\u0161enosti z\u00edskan\u00e9 p\u0159i \u0159e\u0161en\u00ed probl\u00e9m\u016f s v\u00fdkonem, s nimi\u017e se spole\u010dnost Netflix setkala p\u0159i migraci datab\u00e1ze Cassandra z CentOS na Ubuntu v prost\u0159ed\u00edch b\u011b\u017e\u00edc\u00edch na cloudu Amazon EC2 na z\u00e1klad\u011b Xen. Po migraci se z\u00e1t\u011b\u017e na CPU zv\u00fd\u0161ila o 30 % a zpo\u017ed\u011bn\u00ed p\u0159i prov\u00e1d\u011bn\u00ed zapisovac\u00edch operac\u00ed vzrostlo p\u0159ibli\u017en\u011b o tolik. Jak se uk\u00e1zalo, v\u00fdkon aplikac\u00ed, kter\u00e9 intenzivn\u011b vy\u017eaduj\u00ed informace o \u010dase, velmi siln\u011b z\u00e1vis\u00ed na vybran\u00e9m zdroji p\u0159esn\u00e9ho \u010dasu v syst\u00e9mu. <\/p>\n
Zpo\u010d\u00e1tku nebyla p\u0159\u00ed\u010dina sn\u00ed\u017een\u00ed v\u00fdkonu z\u0159ejm\u00e1 a diagnostika za\u010dala sledov\u00e1n\u00edm mo\u017en\u00e9ho vlivu neust\u00e1le b\u011b\u017e\u00edc\u00edch nebo p\u0159\u00edle\u017eitostn\u011b spou\u0161t\u011bn\u00fdch n\u00e1ro\u010dn\u00fdch syst\u00e9mov\u00fdch proces\u016f pomoc\u00ed utilit top a execsnoop. V\u0161echno v\u0161ak ukazovalo na to, \u017ee spot\u0159eba zdroj\u016f vzrostla p\u0159edev\u0161\u00edm v datab\u00e1zi Cassandra, napsan\u00e9 v jazyce Java. Srovn\u00e1n\u00ed profilovac\u00edch v\u00fdsledk\u016f dvou proces\u016f Cassandra, kter\u00e9 byly spu\u0161t\u011bny paraleln\u011b v CentOS a Ubuntu a zpracov\u00e1valy stejn\u00e9 dotazy, uk\u00e1zalo, \u017ee p\u0159ibli\u017en\u011b 32 % celkov\u00e9ho \u010dasu je tr\u00e1veno vol\u00e1n\u00edm os::javaTimeMillis(), pou\u017e\u00edvan\u00e9 k z\u00edsk\u00e1n\u00ed informac\u00ed o aktu\u00e1ln\u00edm \u010dase. <\/p>\n
Po tomto byl proveden experiment, b\u011bhem kter\u00e9ho byla naps\u00e1na jednoduch\u00e1 aplikace v jazyce Java, kter\u00e1 v cyklu volala metodu System.currentTimeMillis() sto milionkr\u00e1t. Spu\u0161t\u011bn\u00ed aplikace uk\u00e1zalo, \u017ee na CentOS k jej\u00edmu proveden\u00ed bylo pot\u0159eba 13 sekund, zat\u00edmco na Ubuntu — p\u0159ibli\u017en\u011b 68 sekund, tedy 5kr\u00e1t pomaleji. V jazyce C byla naps\u00e1na podobn\u00e1 aplikace, kter\u00e1 sto milionkr\u00e1t volala funkci gettimeofday(), ale p\u0159i jej\u00edm prov\u00e1d\u011bn\u00ed byly z\u00edsk\u00e1ny podobn\u00e9 v\u00fdsledky. <\/p>\n
Jakmile bylo jasn\u00e9, \u017ee zdrojem probl\u00e9mu je funkce pro vr\u00e1cen\u00ed aktu\u00e1ln\u00edho \u010dasu, pozornost se obr\u00e1tila na zm\u011bnu ukazatel\u016f p\u0159i v\u00fdb\u011bru r\u016fzn\u00fdch zdroj\u016f p\u0159esn\u00e9ho \u010dasu v syst\u00e9mu. Podle obsahu «\/sys\/devices\/system\/clocksource\/clocksource0\/current_clocksource» byl p\u0159i spu\u0161t\u011bn\u00ed Linuxu ve virtu\u00e1ln\u00edm syst\u00e9mu v\u00fdchoz\u00ed \u010dasova\u010d «xen». Po zm\u011bn\u011b zdroje \u010dasu na «tsc» se \u010das prov\u00e1d\u011bn\u00ed testovac\u00ed aplikace na Ubuntu zkr\u00e1til z 68 na 3,3 sekundy, tedy se zrychlil 20kr\u00e1t. D\u00e1le byl proveden test v\u00fdkonu \u010dasov\u00e9ho zdroje kvm-clock, kter\u00fd uk\u00e1zal zv\u00fd\u0161en\u00ed latenc\u00ed o 20 % v porovn\u00e1n\u00ed s TSC. $ 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
Pro z\u00edsk\u00e1n\u00ed \u010dasu p\u0159i v\u00fdb\u011bru zdroje TSC se pou\u017e\u00edv\u00e1 procesorov\u00fd instrukce RDTSC, jej\u00ed\u017e proveden\u00ed nevy\u017eaduje syst\u00e9mov\u00fd vol\u00e1n\u00ed (instrukce nevy\u017eaduje zv\u00fd\u0161en\u00e9 opr\u00e1vn\u011bn\u00ed a vrac\u00ed hodnotu z vestav\u011bn\u00e9ho \u010dasova\u010de CPU). TSC nen\u00ed ve v\u00fdchoz\u00edm nastaven\u00ed aktivov\u00e1n, proto\u017ee v minulosti tento zdroj neznemo\u017e\u0148oval pomal\u00fd drift \u010dasu, kter\u00fd byl v jin\u00fdch zpracovatel\u00edch softwarov\u011b korigov\u00e1n pro dosa\u017een\u00ed p\u0159esn\u011bj\u0161\u00edch m\u011b\u0159en\u00ed. Podle in\u017een\u00fdra specializuj\u00edc\u00edho se na v\u00fdvoj procesor\u016f obavy o \u010dasov\u00e9 posuny p\u0159i pou\u017e\u00edv\u00e1n\u00ed TSC ji\u017e d\u00e1vno neodpov\u00eddaj\u00ed skute\u010dnosti a modern\u00edch procesorech<\/a> tento zdroj m\u016f\u017ee po l\u00e9ta poskytovat stabiln\u00ed hodnoty. <\/p>\n P\u0159echod k pracovn\u00edmu servery<\/a> v Netflix vedlo pou\u017eit\u00ed TSC ke sn\u00ed\u017een\u00ed latenc\u00ed p\u0159i z\u00e1pisu o 43 % a k dosa\u017een\u00ed v\u00fdsledk\u016f na Ubuntu, kter\u00e9 \u010dty\u0159ikr\u00e1t p\u0159ekonaly konfiguraci s CentOS a \u010dasov\u00fdm zdrojem «xen». V\u00fdsledky proveden\u00e9ho v\u00fdzkumu byly p\u0159ed\u00e1ny spole\u010dnosti Amazon, kter\u00e1 ofici\u00e1ln\u011b doporu\u010dila v prost\u0159ed\u00edch AWS EC2 zalo\u017een\u00fdch na hypervizoru Xen pou\u017e\u00edvat v\u00fdchoz\u00ed \u010dasov\u00fd zdroj TSC (v prost\u0159ed\u00edch zalo\u017een\u00fdch na hypervizoru Nitro z\u016fst\u00e1v\u00e1 doporu\u010den 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\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\udd47Anal\u00fdza vlivu na v\u00fdkon vybran\u00e9ho \u010dasov\u00e9ho zdroje v syst\u00e9mu | ProHoster","description":"Brendan Gregg, jeden z v\u00fdvoj\u00e1\u0159\u016f DTrace, kter\u00fd nyn\u00ed vyv\u00edj\u00ed n\u00e1stroje pro anal\u00fdzu v\u00fdkonu na b\u00e1zi BPF v j\u00e1dru Linux, shrnul zku\u0161enosti z\u00edskan\u00e9 p\u0159i anal\u00fdze probl\u00e9m\u016f s 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Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"