From c7269d0607d835728122271e839416a23e347fbb Mon Sep 17 00:00:00 2001 From: Sridhar Seshasayee Date: Mon, 5 Jun 2023 13:41:28 +0530 Subject: [PATCH] PendingReleaseNotes: Document mClock scheduler fixes and enhancements Signed-off-by: Sridhar Seshasayee (cherry picked from commit 49aad118aa41a8e66ab65f229c5633ee18c6a3b2) Conflicts: PendingReleaseNotes - Modified doc URL to point to reef --- PendingReleaseNotes | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/PendingReleaseNotes b/PendingReleaseNotes index 00ba599c423..02f1c818f40 100644 --- a/PendingReleaseNotes +++ b/PendingReleaseNotes @@ -139,6 +139,29 @@ * CEPHFS: After recovering a Ceph File System post following the disaster recovery procedure, the recovered files under `lost+found` directory can now be deleted. * core: cache-tiering is now deprecated. +* mClock Scheduler: The mClock scheduler (default scheduler in Quincy) has + undergone significant usability and design improvements to address the slow + backfill issue. Some important changes are: + * The 'balanced' profile is set as the default mClock profile because it + represents a compromise between prioritizing client IO or recovery IO. Users + can then choose either the 'high_client_ops' profile to prioritize client IO + or the 'high_recovery_ops' profile to prioritize recovery IO. + * QoS parameters like reservation and limit are now specified in terms of a + fraction (range: 0.0 to 1.0) of the OSD's IOPS capacity. + * The cost parameters (osd_mclock_cost_per_io_usec_* and + osd_mclock_cost_per_byte_usec_*) have been removed. The cost of an operation + is now determined using the random IOPS and maximum sequential bandwidth + capability of the OSD's underlying device. + * Degraded object recovery is given higher priority when compared to misplaced + object recovery because degraded objects present a data safety issue not + present with objects that are merely misplaced. Therefore, backfilling + operations with the 'balanced' and 'high_client_ops' mClock profiles may + progress slower than what was seen with the 'WeightedPriorityQueue' (WPQ) + scheduler. + * The QoS allocations in all the mClock profiles are optimized based on the above + fixes and enhancements. + * For more detailed information see: + https://docs.ceph.com/en/reef/rados/configuration/mclock-config-ref/ >=17.2.1