Write performance latency is getting too high (~6ms) on Sybase database.

Solution Unverified - Updated -

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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