All rados/thrash-erasure-code-big tests that die due to the “wait_for_recovery” timeout have one thing in common: They contain either thrashers/pggrow or thrashers/mapgap.

The difference between pggrow and mapgap vs. all other non-offending thrashers (default, careful, fastread, and morepggrow) is that they lack an override setting for osd max backfills. osd max backfills is the max number of backfill operations allowed to/from an OSD. The higher the number, the quicker the recovery. By default, this value is 1. On all of the non-offending thrashers (default, careful, fastread, and morepggrow), the default 1 value gets overridden in their .yaml files with a value > 1. This is not the case for pggrow and mapgap, however, as they lack an osd max backfills override setting.

The mclock op scheduler is known to override osd max backfills with a high value, but all of the thrash-erasure-code-big thrashers have their op queue set to “debug_random”, which chooses randomly between op queues (the debug_random op queue is set to override the default mclock_scheduler here in qa/config/rados.yaml). So, coupled with the “debug_random” op queue, the low osd max backfill setting is causing some tests to time out in recovery.

WITHOUT osd max backfills, as they are now, “mapgap” and “pggrow” tests die due to timed-out recovery about 17/100 times, as seen here with a pggrow test: http://pulpito.front.sepia.ceph.com/lflores-2022-05-18_14:24:29-rados:thrash-erasure-code-big-master-distro-default-smithi/

WITH osd max backfills specified, as I have suggested in this PR, 99/100 tests passed, with one test failing for a different reason:
http://pulpito.front.sepia.ceph.com/lflores-2022-05-17_22:40:27-rados:thrash-erasure-code-big-master-distro-default-smithi/

I also scheduled 145 tests WITH osd max backfills that are a mix of pggrow and mapgap thrashers. 144/145 tests passed, with one test failing for a different reason. http://pulpito.front.sepia.ceph.com/lflores-2022-05-17_15:27:54-rados:thrash-erasure-code-big-master-distro-default-smithi/

Fixes: https://tracker.ceph.com/issues/51076
Signed-off-by: Laura Flores lflores@redhat.com

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