Brendan Gregg, unul dintre dezvoltatorii DTrace, care dezvolt\u0103 acum instrumente pentru analiza performan\u021bei bazate pe BPF \u00een nucleul Linux, a sintetizat experien\u021ba acumulat\u0103 \u00een analiza problemelor de performan\u021b\u0103 cu care s-a confruntat compania Netflix \u00een timpul migr\u0103rii bazei de date Cassandra de pe CentOS pe Ubuntu \u00een medii rulate pe Amazon EC2 bazate pe Xen. Dup\u0103 migrare, \u00eenc\u0103rcarea CPU a crescut cu 30% \u0219i \u00eent\u00e2rzierile \u00een execu\u021bia opera\u021biunilor de scriere au crescut cam \u00een aceea\u0219i m\u0103sur\u0103. A\u0219a cum s-a dovedit, performan\u021ba aplica\u021biilor care solicit\u0103 intens informa\u021bii despre timp depinde foarte mult de sursa de timp de \u00eencredere aleas\u0103 \u00een sistem. <\/p>\n
La \u00eenceput, cauza sc\u0103derii performan\u021bei nu era evident\u0103, iar diagnosticarea a \u00eenceput prin urm\u0103rirea posibilelor influen\u021be ale proceselor sistemice consumatoare de resurse, care ruleaz\u0103 continuu sau sunt pornite periodic, folosind utilitarele top \u0219i execsnoop. Dar totul indica faptul c\u0103 consumul de resurse a crescut \u00een baza de date Cassandra, scris\u0103 \u00een Java. Compararea m\u0103sur\u0103torilor profil\u0103rii a dou\u0103 procese Cassandra, rulate simultan \u00een CentOS \u0219i Ubuntu, care procesau acelea\u0219i solicit\u0103ri, a ar\u0103tat c\u0103 aproximativ 32% din tot timpul era cheltuit pentru apelarea os::javaTimeMillis(), utilizat\u0103 pentru ob\u021binerea informa\u021biilor despre timpul curent. <\/p>\n
Dup\u0103 aceea a fost realizat un experiment, \u00een cadrul c\u0103ruia a fost scris\u0103 o aplica\u021bie simpl\u0103 \u00een limbajul Java, care a apelat de o sut\u0103 de milioane de ori metoda System.currentTimeMillis(). Executarea aplica\u021biei a ar\u0103tat c\u0103 \u00een CentOS a fost necesar 13 secunde pentru a o rula, iar \u00een Ubuntu - aproximativ 68 de secunde, adic\u0103 de 5 ori mai lent. O program\u0103 similar\u0103 a fost scris\u0103 \u00een C, apel\u00e2nd de o sut\u0103 de milioane de ori func\u021bia gettimeofday(), dar rezultatele ob\u021binute au fost similare. <\/p>\n
Deoarece a devenit clar c\u0103 sursa problemei este func\u021bia de returnare a timpului curent, aten\u021bia s-a concentrat pe modificarea indicatorilor prin alegerea \u00een sistem a diferitelor surse de timp precis. Judec\u00e2nd dup\u0103 con\u021binutul \u201e\/sys\/devices\/system\/clocksource\/clocksource0\/current_clocksource\u201d, \u00een mod implicit, la pornirea Linux \u00een sistemul gazd\u0103, a fost utilizat temporizatorul \u201exen\u201d. Dup\u0103 schimbarea sursei de timp la \u201etsc\u201d, timpul de execu\u021bie al aplica\u021biei de testare \u00een Ubuntu a sc\u0103zut de la 68 la 3.3 secunde, adic\u0103 a devenit de 20 de ori mai rapid. De asemenea, a fost efectuat un test de performan\u021b\u0103 a sursei de timp kvm-clock, care a ar\u0103tat o cre\u0219tere a \u00eent\u00e2rzierilor cu 20% \u00een compara\u021bie cu 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
Pentru a ob\u021bine timpul prin alegerea sursei TSC, se folose\u0219te instruc\u021biunea procesorului RDTSC, al c\u0103rei execu\u021bie nu necesit\u0103 efectuarea unui apel de sistem (instruc\u021biunea nu necesit\u0103 privilegii \u00eenalte \u0219i furnizeaz\u0103 o valoare din contorul de timp \u00eencorporat \u00een CPU). \u00cen mod implicit, TSC nu este activat deoarece, \u00een trecut, aceast\u0103 surs\u0103 nu excludea driftele treptate de timp, care \u00een alte handler-uri erau corectate prin software pentru a ob\u021bine m\u0103sur\u0103tori mai precise. Potrivit unui inginer specializat \u00een dezvoltarea de procesoare, \u00eengrijor\u0103rile legate de devierile de timp atunci c\u00e2nd se folose\u0219te TSC nu mai sunt relevante \u0219i \u00een procesoarele moderne<\/a> aceast\u0103 surs\u0103 poate oferi valori stabile timp de ani. <\/p>\n Conversia sarcinilor servere<\/a> \u00een Netflix, trecerea la sursa TSC a condus la o reducere a \u00eent\u00e2rzierilor la scriere cu 43% \u0219i la ob\u021binerea \u00een utilizarea Ubuntu a unor rezultate de 4 ori superioare configura\u021biei cu CentOS folosind sursa de timp \u201exen\u201d. Rezultatele studiului efectuat au fost transmise companiei Amazon, care a recomandat oficial ca \u00een mediile AWS EC2 bazate pe hipervizorul Xen s\u0103 se utilizeze implicit sursa de timp TSC (\u00een mediile bazate pe hipervizorul Nitro, kvm-clock r\u0103m\u00e2ne recomandat). \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\udd47Analiza impactului asupra performan\u021bei sursei de timp selectate \u00een sistem | ProHoster","description":"Brendan Gregg, unul dintre dezvoltatorii DTrace, care acum dezvolt\u0103 instrumente pentru analiza performan\u021bei bazate pe BPF \u00een nucleul Linux, a sintetizat experien\u021ba ob\u021binut\u0103 prin analiza problemelor de 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Sursa: opennet.ro<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"