Brendan Gregg, a developer of DTrace, who is now developing performance analysis tools based on BPF in the Linux kernel, summarized the experience gained while examining performance issues that Netflix faced when migrating the Cassandra database from CentOS to Ubuntu in Amazon EC2 cloud environments based on Xen. After the migration, CPU load increased by 30%, and latency for write operations increased by approximately the same amount. It turned out that the performance of applications that heavily query time information is highly dependent on the chosen time source in the system. <\/p>\n
Initially, the cause of the performance degradation was not obvious, and diagnostics began by tracking the possible influence of always-running or periodically launched resource-intensive system processes using the top and execsnoop utilities. However, everything pointed to the fact that resource consumption increased specifically in the Cassandra database written in Java. A comparison of profiling metrics for two Cassandra processes running in parallel on CentOS and Ubuntu, handling the same queries, showed that approximately 32% of the total time was spent on the os::javaTimeMillis() call, which is used to obtain the current time information. <\/p>\n
Ezut\u00e1n k\u00eds\u00e9rletet v\u00e9geztek, amely sor\u00e1n egy egyszer\u0171 Java alkalmaz\u00e1st \u00edrtak, amely egy ciklusban sz\u00e1zmilli\u00f3szor h\u00edvta meg a System.currentTimeMillis() met\u00f3dust. Az alkalmaz\u00e1s futtat\u00e1sa sor\u00e1n kider\u00fclt, hogy CentOS alatt a v\u00e9grehajt\u00e1s\u00e1hoz 13 m\u00e1sodpercre volt sz\u00fcks\u00e9g, m\u00edg Ubuntu alatt k\u00f6r\u00fclbel\u00fcl 68 m\u00e1sodpercet vett ig\u00e9nybe, azaz \u00f6tsz\u00f6r lassabb volt. Egy hasonl\u00f3 programot \u00edrtak C nyelven is, amely sz\u00e1zmilli\u00f3szor h\u00edvta meg a gettimeofday() f\u00fcggv\u00e9nyt, de ennek v\u00e9grehajt\u00e1sa is hasonl\u00f3 eredm\u00e9nyeket mutatott. <\/p>\n
Miut\u00e1n vil\u00e1goss\u00e1 v\u00e1lt, hogy a probl\u00e9ma forr\u00e1sa a jelenlegi id\u0151t visszaad\u00f3 f\u00fcggv\u00e9ny, a figyelem a k\u00fcl\u00f6nb\u00f6z\u0151 pontos id\u0151forr\u00e1sok kiv\u00e1laszt\u00e1sakor bek\u00f6vetkez\u0151 v\u00e1ltoz\u00e1sokra terel\u0151d\u00f6tt. A '\/sys\/devices\/system\/clocksource\/clocksource0\/current_clocksource' tartalma alapj\u00e1n alap\u00e9rtelmez\u00e9s szerint a Linux vend\u00e9g rendszerben az 'xen' id\u0151z\u00edt\u0151t haszn\u00e1lt\u00e1k. Az id\u0151forr\u00e1s 'tsc'-ra v\u00e1ltoztat\u00e1s\u00e1val az Ubuntu alatt tesztelt alkalmaz\u00e1s v\u00e9grehajt\u00e1si ideje 68 m\u00e1sodpercr\u0151l 3,3 m\u00e1sodpercre cs\u00f6kkent, azaz h\u00faszszor gyorsabb lett. Ezen k\u00edv\u00fcl tesztelt\u00e9k az 'kvm-clock' id\u0151forr\u00e1st, amely 20%-os k\u00e9sleked\u00e9st mutatott a TSC-hez k\u00e9pest. $ 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
A TSC forr\u00e1s kiv\u00e1laszt\u00e1sakor az id\u0151 megszerz\u00e9s\u00e9hez a RDTSC processzor utas\u00edt\u00e1st haszn\u00e1lj\u00e1k, amelynek v\u00e9grehajt\u00e1sa nem ig\u00e9nyel rendszerh\u00edv\u00e1st (az utas\u00edt\u00e1s nem ig\u00e9nyel emelt szint\u0171 jogosults\u00e1gokat, \u00e9s az integr\u00e1lt CPU id\u0151m\u00e9r\u0151b\u0151l adja meg az \u00e9rt\u00e9ket). Alap\u00e9rtelmez\u00e9s szerint a TSC nem aktiv\u00e1l\u00f3dik, mivel r\u00e9gebben ez a forr\u00e1s nem z\u00e1rta ki az id\u0151 fokozatos driftj\u00e9t, amely m\u00e1s kezel\u0151kben programoz\u00e1s \u00fatj\u00e1n van korrig\u00e1lva a pontosabb m\u00e9r\u00e9sek el\u00e9r\u00e9s\u00e9hez. A processzorok fejleszt\u00e9s\u00e9re szakosodott m\u00e9rn\u00f6k v\u00e9lem\u00e9nye szerint a TSC haszn\u00e1lat\u00e1val kapcsolatos id\u0151eltol\u00f3d\u00e1sokr\u00f3l val\u00f3 aggodalmak m\u00e1r r\u00e9g\u00f3ta nem aktu\u00e1lisak, \u00e9s a modern processzorok<\/a> ez a forr\u00e1s \u00e9vekig stabil \u00e9rt\u00e9keket szolg\u00e1ltathat. <\/p>\n A TSC forr\u00e1sra val\u00f3 \u00e1tt\u00e9r\u00e9s szerverek<\/a> A Netflix TSC forr\u00e1shoz val\u00f3 \u00e1t\u00e1ll\u00e1sa 43%-kal cs\u00f6kkentette a k\u00e9sleked\u00e9seket a felv\u00e9tel sor\u00e1n, \u00e9s Ubuntu haszn\u00e1lat\u00e1val olyan eredm\u00e9nyeket \u00e9rt el, amelyek n\u00e9gyszer fel\u00fclm\u00falt\u00e1k a CentOS konfigur\u00e1ci\u00f3j\u00e1t, amely az 'xen' id\u0151forr\u00e1st haszn\u00e1lta. A v\u00e9gzett kutat\u00e1s eredm\u00e9nyeit tov\u00e1bb\u00edtott\u00e1k az Amazonnak, amely hivatalosan aj\u00e1nlotta, hogy az AWS EC2 k\u00f6rnyezeteiben, Xen hypervisor alapj\u00e1n az alap\u00e9rtelmezett id\u0151forr\u00e1sk\u00e9nt a TSC-t alkalmazz\u00e1k (a Nitro hypervisoron alapul\u00f3 k\u00f6rnyezetben tov\u00e1bbra is a kvm-clock aj\u00e1nlott). \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\udd47A rendszerben v\u00e1lasztott id\u0151forr\u00e1s teljes\u00edtm\u00e9nyre gyakorolt hat\u00e1s\u00e1nak elemz\u00e9se | ProHoster","description":"Brendan Gregg, az DTrace egyik fejleszt\u0151je, aki jelenleg a Linux kernel BPF alap\u00fa teljes\u00edtm\u00e9nyanaliz\u00e1l\u00f3 eszk\u00f6zeinek fejleszt\u00e9s\u00e9n dolgozik, \u00f6sszefoglalta a teljes\u00edtm\u00e9nnyel 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Forr\u00e1s: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"