{"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\/sk\/blog\/news\/razrabotchik-io_uring-vyyavil-v-qemu-problemu-v-50-80-raz-zamedlyavshuyu-fdmon-v-rezhime-prostoya","title":{"rendered":"V\u00fdvoj\u00e1r io_uring odhalil v QEMU probl\u00e9m, ktor\u00fd spoma\u013eoval fdmon v re\u017eime ne\u010dinnosti 50-80 kr\u00e1t.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Jens Axboe, creator of io_uring and I\/O schedulers CFQ, Deadline, and Noop, proposed a patch for inclusion in the QEMU emulator codebase that reduces latency by 50-80 times when using fdmon (file descriptor monitoring) in the 'aio=io_uring' mode and when the system is in an idle state. <\/p>\n

Probl\u00e9m sa objavil kv\u00f4li pr\u00edli\u0161 r\u00fdchlemu prechodu oper\u00e1cie ppoll() do stavu sp\u00e1nku s \u010dasov\u00fdm obmedzen\u00edm 499 ms, aj ke\u010f bol pr\u00edtomn\u00fd vstup\/v\u00fdstup. Na obnovenie vykon\u00e1vania hlavn\u00e9ho cyklu spracovania udalost\u00ed, ktor\u00e9 bolo pozastaven\u00e9 kv\u00f4li ppoll(), bol navrhnut\u00fd patch, ktor\u00fd prid\u00e1va do funkcie na vytvorenie z\u00e1znamu SQE (Submission Queue Entry) volanie funkcie aio_notify(), ktor\u00e1 prebud\u00ed ppoll() z re\u017eimu sp\u00e1nku. <\/p>\n

Probl\u00e9m sa objavil pri regresnom testovan\u00ed io_uring v virtu\u00e1lnych strojoch<\/a> with various block devices. Jens noted the occasional appearance of timeouts when using AHCI\/SATA devices in 'aio=io_uring' mode, while tests with virtio-blk or NVMe devices consistently completed successfully in about a second. It was observed that the issue affects all types of block devices, but latency is most pronounced for AHCI\/SATA devices due to the use of MMIO. <\/p>\n

Jens tie\u017e op\u00edsal svoje sk\u00fasenosti s laden\u00edm probl\u00e9mu pomocou AI asistenta Claude. Po identifik\u00e1cii scen\u00e1ra reprodukuj\u00faceho podmienky na vznik \u010dasov\u00e9ho obmedzenia odovzdal dostupn\u00e9 ladacie \u00fadaje Claude, poskytol pr\u00edstup k virtu\u00e1lnemu stroju a navrhol identifikova\u0165 pravdepodobn\u00e9 pr\u00ed\u010diny zisten\u00e9ho zlyhania. <\/p>\n

Claude decided to test whether performance would degrade when using a virtio-blk device and executed a destructive scenario proposed by the developer that reproduced the issue. During the test, the first 128 MB of content was deleted from the block device \/dev\/vda in the virtual machine. After this, Claude concluded that the problem was not with virtio-blk. When Jens pointed out the deletion of part of the content from \/dev\/vda to the AI assistant, it replied, 'Yes, I did that,' and after a request to fix it, restored the functionality of the virtual disk \/dev\/vda. It was noted that the use of the AI assistant helped to better understand the peculiarities of executing various event processing loops in QEMU. <\/p>\n

Je pozoruhodn\u00e9, \u017ee probl\u00e9m bolo dos\u0165 \u0165a\u017ek\u00e9 odhali\u0165, preto\u017ee v syntetick\u00fdch testoch sa spomalenie nezaznamen\u00e1va kv\u00f4li tomu, \u017ee na vznik poruchy vpl\u00fdva prebudenie cyklu spracovania udalost\u00ed s ppoll z inej aktivity, a syntetick\u00e9 testy vstupu\/v\u00fdstupu nevykon\u00e1vaj\u00fa spracovanie prijat\u00fdch \u00fadajov. Spomalenie sa stalo viac vidite\u013en\u00fdm, ke\u010f sme pridali nieko\u013eko volan\u00ed usleep() na simul\u00e1ciu spracovania \u00fadajov. <\/p>\n

Pred opravou na syst\u00e9me v ne\u010dinnosti (idle): time sudo .\/iotest \/dev\/sda Vykonan\u00e9 za 25.76 sekundy fish extern\u00e9 usr \u010das 6.19 millis 783.00 mikros 5.41 millis sys \u010das 12.43 millis 642.00 mikros 11.79 millis <\/p>\n

Po oprave na syst\u00e9me v ne\u010dinnosti: time sudo .\/iotest \/dev\/sda Vykonan\u00e9 za 1.30 sekundy fish extern\u00e9 usr \u010das 2.14 millis 0.14 millis 2.00 millis sys \u010das 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\u00e1r io_uring odhalil v QEMU probl\u00e9m, ktor\u00fd 50-80 kr\u00e1t spoma\u013eoval fdmon v re\u017eime ne\u010dinnosti | ProHoster","description":"Jens Axboe, tvorca io_uring a pl\u00e1nova\u010dov vstupu\/v\u00fdstupu CFQ, Deadline a Noop, navrhol na zahrnutie do k\u00f3dovej z\u00e1kladne emul\u00e1tora QEMU patch, ktor\u00fd zni\u017euje oneskorenia pri pr\u00e1ci fdmon (file) 50-80 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