{"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\/da\/blog\/news\/razrabotchik-io_uring-vyyavil-v-qemu-problemu-v-50-80-raz-zamedlyavshuyu-fdmon-v-rezhime-prostoya","title":{"rendered":"Udvikleren af io_uring har identificeret et problem i QEMU, der forsinker fdmon 50-80 gange i tomgangsmodus.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Jens Axboe, skaberen af io_uring og planl\u00e6ggere for ind- og uddata, CFQ, Deadline og Noop, har foresl\u00e5et en patch til at inkludere i QEMU-emulatorens kodebase, der reducerer forsinkelser ved fdmon (file descriptor monitoring) i tilstanden 'aio=io_uring' med 50-80 gange, mens systemet er i idle. <\/p>\n

Problemet opstod p\u00e5 grund af overgangen af operationen ppoll() til s\u00f8vntilstand med en timeout p\u00e5 499 ms, p\u00e5 trods af at der var I\/O-aktiviteter. For at genoptage hovedbegivenhedscyklussen, der blev pauset p\u00e5 grund af ppoll(), blev der foresl\u00e5et en patch, som tilf\u00f8jede et kald til aio_notify()-funktionen i funktionen til at oprette SQE (Submission Queue Entry), hvilket v\u00e6kkede ppoll() fra s\u00f8vntilstand. <\/p>\n

Problemet dukkede op under regressions-testning af io_uring med virtuelle maskiner<\/a> med forskellige bloklagringsenheder. Jens har bem\u00e6rket tilf\u00e6ldige timeouts ved brug af AHCI\/SATA-enheder i 'aio=io_uring' tilstand, mens tests med virtio-blk eller nvme-enheder altid blev gennemf\u00f8rt med succes p\u00e5 cirka et sekund. Det bem\u00e6rkes, at problemet p\u00e5virker alle typer bloklagringsenheder, men for AHCI\/SATA-enheder er fremkomsten af forsinkelser mest udtalt p\u00e5 grund af brugen af MMIO. <\/p>\n

Jens beskrev ogs\u00e5 sin erfaring med at fejlfinde problemet ved hj\u00e6lp af AI-assistenten Claude. Efter at have identificeret et scenarie, der gentager betingelserne for opst\u00e5en af timeout, delte han de tilg\u00e6ngelige fejlfindingsdata med Claude, gav adgang til den virtuelle maskine og foreslog at identificere de mulige \u00e5rsager til det identificerede problem. <\/p>\n

Claude besluttede at teste, om ydeevnen ville blive reduceret, n\u00e5r der bruges en virtio-blk enhed, og k\u00f8rte et destruktivt scenarie, der reproducerede problemet. Under testen blev de f\u00f8rste 128 MB indhold slettet fra blokenheden \/dev\/vda i den virtuelle maskine. Efterf\u00f8lgende konkluderede Claude, at problemet ikke var i virtio-blk. Da Jens bad AI-assistenten om at slette en del af indholdet fra \/dev\/vda, svarede den 'Ja, det gjorde jeg', og efter en anmodning om at rette det, genoprettede den funktionaliteten til den virtuelle disk \/dev\/vda. Det bem\u00e6rkes, at brugen af AI-assistenten har hjulpet med bedre at forst\u00e5 de forskellige cykler af begivenhedsbehandling i QEMU. <\/p>\n

Bem\u00e6rkelsesv\u00e6rdigt er det, at problemet var ret sv\u00e6rt at opdage, da forsinkelsen ikke registreres i syntetiske tests, fordi opv\u00e5gningen af event-loopet med ppoll p\u00e5virkes af anden aktivitet, og syntetiske input\/output tests behandler ikke de modtagne data. Forsinkelsen blev mere m\u00e6rkbar ved at tilf\u00f8je flere opkald til usleep() for at simulere databehandling. <\/p>\n

F\u00f8r rettelsen p\u00e5 systemet i en inaktiv tilstand:\u00a0 \u00a0 \u00a0 time sudo .\/iotest \/dev\/sda\u00a0 \u00a0 \u00a0 Utf\u00f8rt p\u00e5\u00a0 25.76 sekunder\u00a0 \u00a0 \u00a0 fish\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 ekstern\u00a0 \u00a0 \u00a0 usr tid\u00a0 \u00a0 6.19 millis\u00a0 783.00 micros\u00a0 5.41 millis\u00a0 \u00a0 \u00a0 sys tid\u00a0 12.43 millis\u00a0 642.00 micros\u00a0 11.79 millis <\/p>\n

Efter rettelsen p\u00e5 systemet i en inaktiv tilstand:\u00a0 \u00a0 \u00a0 time sudo .\/iotest \/dev\/sda\u00a0 \u00a0 \u00a0 Utf\u00f8rt p\u00e5\u00a0 \u00a0 1.30 sekunder\u00a0 \u00a0 \u00a0 fish\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 ekstern\u00a0 \u00a0 \u00a0 usr tid\u00a0 \u00a0 2.14 millis\u00a0 \u00a0 0.14 millis\u00a0 \u00a0 2.00 millis\u00a0 \u00a0 \u00a0 sys tid\u00a0 16.93 millis\u00a0 \u00a0 1.16 millis\u00a0 15.76 millis
\n
Kilde: 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\udd47Udvikler af io_uring har identificeret et problem i QEMU, der 50-80 gange forsinkede fdmon i inaktiv tilstand | ProHoster","description":"Jens Axboe, skaberen af io_uring og input\/output-planl\u00e6ggere CFQ, Deadline og Noop, har foresl\u00e5et at inkludere en patch i kodebasen for emulatoren QEMU, som reducerer forsinkelsen ved fdmon (fil) med 50-80 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