Write performance latency is getting too high (~6ms) on Sybase database.
Issue
- Write performance latency is getting too high (~6ms) on Sybase database. Expectations is < 1ms.
1. 6ms /io => sybase directio | xfs | lvm striped .or. single disk lvm | vmware vmdk <= too slow
2. 0.4-0.7ms /io => sybase directio | | lvm striped .or. raw non-lvm disk| vmware vmdk <= says "raw fs"?
3. 0.007ms /io => sybase bufferio | | lvm striped .or. raw non-lvm disk| vmware vmdk <= (kern cache only)
- The below changes on the scheduler knobs have fixed the issue:
From:
sysctl kernel.sched_min_granularity_ns=10000000
sysctl kernel.sched_wakeup_granularity_ns=15000000
To:
sysctl kernel.sched_min_granularity_ns=3000000
sysctl kernel.sched_wakeup_granularity_ns=4000000
Environment
- Red Hat Enterprise Linux 7.8
- RHEL guest on VMware hypervisor
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