{"id":161903,"date":"2026-02-20T17:11:55","date_gmt":"2026-02-20T15:11:55","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/razrabotchik-io_uring-vyyavil-v-qemu-problemu-v-50-80-raz-zamedlyavshuyu-fdmon-v-rezhime-prostoya"},"modified":"2026-02-20T17:11:55","modified_gmt":"2026-02-20T15:11:55","slug":"razrabotchik-io_uring-vyyavil-v-qemu-problemu-v-50-80-raz-zamedlyavshuyu-fdmon-v-rezhime-prostoya","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/news\/razrabotchik-io_uring-vyyavil-v-qemu-problemu-v-50-80-raz-zamedlyavshuyu-fdmon-v-rezhime-prostoya","title":{"rendered":"V\u00fdvoj\u00e1\u0159 io_uring odhalil v QEMU probl\u00e9m, kter\u00fd zpomaloval fdmon v re\u017eimu ne\u010dinnosti 50-80kr\u00e1t.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Jens Axboe, tv\u016frce io_uring a pl\u00e1nova\u010d\u016f vstupu\/v\u00fdstupu CFQ, Deadline a Noop, navrhl za\u010dlen\u011bn\u00ed patchi do k\u00f3du emul\u00e1toru QEMU, kter\u00fd zkracuje latenci o 50-80 % p\u0159i pou\u017eit\u00ed fdmon (monitorov\u00e1n\u00ed deskriptoru souboru) v re\u017eimu aio=io_uring<\/a> a p\u0159i ne\u010dinnosti syst\u00e9mu. <\/p>\n

Probl\u00e9m se projevoval p\u0159i p\u0159evodu operace ppoll() do stavu sp\u00e1nku s \u010dasov\u00fdm limitem 499 ms, i kdy\u017e byl k dispozici vstup\/v\u00fdstup. Pro obnoven\u00ed hlavn\u00edho zpracovatelsk\u00e9ho cyklu, kter\u00fd byl pozastaven kv\u016fli ppoll(), byl navr\u017een patch, kter\u00fd p\u0159id\u00e1v\u00e1 do funkce pro vytv\u00e1\u0159en\u00ed z\u00e1znamu SQE (Submission Queue Entry) vol\u00e1n\u00ed funkce aio_notify(), kter\u00e1 probud\u00ed ppoll() ze stavu sp\u00e1nku. <\/p>\n

Probl\u00e9m se objevil p\u0159i regresn\u00edm testov\u00e1n\u00ed io_uring s virtual machines<\/a> s r\u016fzn\u00fdmi blokov\u00fdmi za\u0159\u00edzen\u00edmi. Jens si v\u0161iml n\u00e1hodn\u00e9ho v\u00fdskytu timeout\u016f p\u0159i pou\u017eit\u00ed za\u0159\u00edzen\u00ed AHCI\/SATA v re\u017eimu aio=io_uring<\/a>, zat\u00edmco v konfigurac\u00edch s za\u0159\u00edzen\u00edmi virtio-blk nebo nvme testy v\u017edy \u00fasp\u011b\u0161n\u011b prob\u00edhaly za p\u0159ibli\u017en\u011b jednu sekundu. Je d\u00e1le poznamen\u00e1no, \u017ee probl\u00e9m se t\u00fdk\u00e1 v\u0161ech typ\u016f blokov\u00fdch za\u0159\u00edzen\u00ed, av\u0161ak u za\u0159\u00edzen\u00ed AHCI\/SATA se zpo\u017ed\u011bn\u00ed projevuje nejv\u00edce kv\u016fli pou\u017eit\u00ed MMIO. <\/p>\n

Jens tak\u00e9 popsal svou zku\u0161enost s lad\u011bn\u00edm probl\u00e9mu pomoc\u00ed AI asistenta Claude. Po ur\u010den\u00ed sc\u00e9n\u00e1\u0159e, kter\u00fd reprodukoval podm\u00ednky vedouc\u00ed k v\u00fdskytu \u010dasov\u00e9ho limitu, p\u0159edal dostupn\u00e9 ladic\u00ed \u00fadaje Claudovi, poskytl p\u0159\u00edstup k virtu\u00e1ln\u00edmu po\u010d\u00edta\u010di a navrhl, aby ur\u010dil pravd\u011bpodobn\u00e9 p\u0159\u00ed\u010diny zji\u0161t\u011bn\u00e9 chyby. <\/p>\n

Claude se rozhodl otestovat, zda dojde k zpomalen\u00ed p\u0159i pou\u017eit\u00ed za\u0159\u00edzen\u00ed virtio-blk, a spustil s n\u00edm navr\u017een\u00fd destruktivn\u00ed sc\u00e9n\u00e1\u0159, kter\u00fd reprodukoval probl\u00e9m. B\u011bhem testu byly odstran\u011bny prvn\u00ed 128 MB obsahu z blokov\u00e9ho za\u0159\u00edzen\u00ed \/dev\/vda ve virtu\u00e1ln\u00edm stroji. Pot\u00e9 Claude dosp\u011bl k z\u00e1v\u011bru, \u017ee probl\u00e9m nesouvis\u00ed s virtio-blk. Kdy\u017e Jens upozornil AI asistenta na odstran\u011bn\u00ed \u010d\u00e1sti obsahu \/dev\/vda, odpov\u011bd\u011bl 'Ano, ud\u011blal jsem to', a po \u017e\u00e1dosti o opravu obnovil funk\u010dnost virtu\u00e1ln\u00edho disku \/dev\/vda. Je poznamen\u00e1no, \u017ee pou\u017eit\u00ed AI asistenta pomohlo l\u00e9pe pochopit vlastnosti vykon\u00e1v\u00e1n\u00ed r\u016fzn\u00fdch cykl\u016f zpracov\u00e1n\u00ed ud\u00e1lost\u00ed v QEMU. <\/p>\n

Je pozoruhodn\u00e9, \u017ee probl\u00e9m bylo obt\u00ed\u017en\u00e9 odhalit, proto\u017ee ve syntetick\u00fdch testech se zpomalen\u00ed nepotvrzuje, jeliko\u017e na v\u00fdskyt chyby m\u00e1 vliv probuzen\u00ed cyklu zpracov\u00e1n\u00ed ud\u00e1lost\u00ed pomoc\u00ed ppoll kv\u016fli jin\u00e9 aktivit\u011b, a syntetick\u00e9 testy vstupu\/v\u00fdstupu nezpracov\u00e1vaj\u00ed p\u0159ijat\u00e1 data. Zpomalen\u00ed se stalo v\u00fdrazn\u011bj\u0161\u00ed p\u0159i p\u0159id\u00e1n\u00ed n\u011bkolika vol\u00e1n\u00ed usleep() pro simulaci zpracov\u00e1n\u00ed dat. <\/p>\n

P\u0159ed opravou na syst\u00e9mu v ne\u010dinn\u00e9m stavu (idle): time sudo .\/iotest \/dev\/sda Provedeno za 25.76 sekundy fish extern\u00ed usr time 6.19 millis 783.00 micros 5.41 millis sys time 12.43 millis 642.00 micros 11.79 millis <\/p>\n

Po oprav\u011b na syst\u00e9mu v ne\u010dinn\u00e9m stavu: time sudo .\/iotest \/dev\/sda Provedeno za 1.30 sekundy fish extern\u00ed usr time 2.14 millis 0.14 millis 2.00 millis sys time 16.93 millis 1.16 millis 15.76 millis
\n
Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0419\u0435\u043d\u0441 \u042d\u043a\u0441\u0431\u043e (Jens Axboe), \u0441\u043e\u0437\u0434\u0430\u0442\u0435\u043b\u044c io_uring \u0438 \u043f\u043b\u0430\u043d\u0438\u0440\u043e\u0432\u0449\u0438\u043a\u043e\u0432 \u0432\u0432\u043e\u0434\u0430\/\u0432\u044b\u0432\u043e\u0434\u0430 CFQ, Deadline \u0438 Noop, \u043f\u0440\u0435\u0434\u043b\u043e\u0436\u0438\u043b \u0434\u043b\u044f \u0432\u043a\u043b\u044e\u0447\u0435\u043d\u0438\u044f \u0432 \u043a\u043e\u0434\u043e\u0432\u0443\u044e \u0431\u0430\u0437\u0443 \u044d\u043c\u0443\u043b\u044f\u0442\u043e\u0440\u0430 QEMU \u043f\u0430\u0442\u0447, \u0432 50-80 \u0440\u0430\u0437 \u0441\u043e\u043a\u0440\u0430\u0449\u0430\u044e\u0449\u0438\u0439 \u0437\u0430\u0434\u0435\u0440\u0436\u043a\u0438 \u043f\u0440\u0438 \u0440\u0430\u0431\u043e\u0442\u0435 fdmon (file descriptor monitoring) \u0432 \u0440\u0435\u0436\u0438\u043c\u0435 «aio=io_uring» \u0438 \u043d\u0430\u0445\u043e\u0436\u0434\u0435\u043d\u0438\u0438 \u0441\u0438\u0441\u0442\u0435\u043c\u044b \u0432 \u0441\u043e\u0441\u0442\u043e\u044f\u043d\u0438\u0438 \u043f\u0440\u043e\u0441\u0442\u043e\u044f (idle). \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u043f\u0440\u043e\u044f\u0432\u043b\u044f\u043b\u0430\u0441\u044c \u0438\u0437-\u0437\u0430 \u043f\u0435\u0440\u0435\u0432\u043e\u0434\u0430 \u043e\u043f\u0435\u0440\u0430\u0446\u0438\u0438 ppoll() \u0432 \u0441\u043e\u0441\u0442\u043e\u044f\u043d\u0438\u0438 \u0441\u043d\u0430 \u0441 \u0442\u0430\u0439\u043c\u0430\u0443\u0442\u043e\u043c 499 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":8,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-161903","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\udd47V\u00fdvoj\u00e1\u0159 io_uring odhalil v QEMU probl\u00e9m, kter\u00fd zpomaloval fdmon v ne\u010dinn\u00e9m re\u017eimu 50\u201380kr\u00e1t | ProHoster","description":"Jens Axboe, tv\u016frce io_uring a pl\u00e1nova\u010d\u016f vstupu\/v\u00fdstupu CFQ, Deadline a Noop, navrhl pro za\u010dlen\u011bn\u00ed do k\u00f3dov\u00e9 z\u00e1kladny emul\u00e1toru QEMU patch, kter\u00fd sni\u017euje latence p\u0159i pr\u00e1ci s 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