{"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\/ro\/blog\/news\/razrabotchik-io_uring-vyyavil-v-qemu-problemu-v-50-80-raz-zamedlyavshuyu-fdmon-v-rezhime-prostoya","title":{"rendered":"Dezvoltatorul io_uring a identificat o problem\u0103 \u00een QEMU care \u00eencetinea fdmon cu 50-80 de ori \u00een modul de repaus.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

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

The issue arose due to the translation of the ppoll() operation into a sleep state with a timeout of 499 ms, despite the presence of input\/output. To resume the main event processing loop, which was being paused due to ppoll(), a patch was proposed that adds a call to the aio_notify() function in the SQE (Submission Queue Entry) creation function. <\/p>\n

The problem emerged during regression testing of io_uring with virtu\u00e1lne ma\u0161ini<\/a> with various block devices. Jens noted an 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 is noted that the problem affects all types of block devices, but for AHCI\/SATA devices, the appearance of delays is most pronounced due to the use of MMIO. <\/p>\n

Jens also described his experience debugging the problem using the AI assistant Claude. After defining the scenario that reproduced the conditions for a timeout, he provided the existing debug data to Claude, granted access to the virtual machine, and suggested identifying the probable causes of the detected failure. <\/p>\n

Claude decided to check if performance would degrade with the virtio-blk device and ran a destructive scenario proposed by the developer that reproduces 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 to the AI assistant the deletion of part of the content from \/dev\/vda, it responded «Yes, I did that», and after a request to fix it, restored the functionality of the virtual disk \/dev\/vda. It is noted that using the AI assistant helped better understand the nuances of event processing cycles in QEMU. <\/p>\n

Este demn de men\u021bionat c\u0103 problema a fost destul de greu de descoperit, deoarece \u00een testele sintetice, \u00eent\u00e2rzierile nu sunt \u00eenregistrate datorit\u0103 influen\u021bei asupra apari\u021biei erorilor, generat de trezirea ciclului de procesare a evenimentelor cu ppoll din cauza unei alte activit\u0103\u021bi, iar testele sintetice de intrare\/ie\u0219ire nu proceseaz\u0103 datele primite. \u00cent\u00e2rzierea a devenit mai vizibil\u0103 odat\u0103 cu ad\u0103ugarea mai multor apeluri usleep() pentru a simula procesarea datelor. <\/p>\n

Dup\u0103 corectare, \u00een sistemul \u00een stare de inactivitate (idle): time sudo .\/iotest \/dev\/sda Executat \u00een 25.76 secs fish extern usr time 6.19 millis 783.00 micros 5.41 millis sys time 12.43 millis 642.00 micros 11.79 millis <\/p>\n

Dup\u0103 corectare, \u00een sistemul \u00een stare de inactivitate: time sudo .\/iotest \/dev\/sda Executat \u00een 1.30 secs fish extern usr time 2.14 millis 0.14 millis 2.00 millis sys time 16.93 millis 1.16 millis 15.76 millis
\n
Sursa: opennet.ro<\/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\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\udd47Dezvoltatorul io_uring a identificat o problem\u0103 \u00een QEMU, care \u00eencetinea fdmon de 50-80 de ori \u00een modul de inactivitate | ProHoster","description":"Jens Axboe, creatorul io_uring \u0219i al planificatorilor de intrare\/ie\u0219ire CFQ, Deadline \u0219i Noop, a propus includerea \u00eentr-un patch care reduce \u00eent\u00e2rzierile de 50-80 de ori \u00een timpul func\u021bion\u0103rii fdmon (file) \u00een 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