** Changed in: linux (Ubuntu Bionic)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1794165
Title:
hisi_sas: Reduce unnecessary spin lock contention
Status in linux package in Ubuntu:
Fix Committed
Status in linux source package in Bionic:
Fix Committed
Status in linux source package in Cosmic:
Fix Committed
Bug description:
[Impact]
The current design of hisi_sas_task_prep() has two critical sections
protected by different spin locks. This can lead to unnecessary thrashing. By
merging the critical sections under one spin lock, we can avoid this.
[Test Case]
Use fio to measure performance difference, and verify that there is no
performance decrease. Sample config attached. Test on D05 and D06 systems,
since both are impacted.
[Fix]
commit 6cca51ee0aa2540d648ff8698c3889330d897f27
Author: Xiang Chen <[email protected]>
Date: Wed Jul 18 22:14:31 2018 +0800
scsi: hisi_sas: Tidy hisi_sas_task_prep()
[Regression Risk]
It's possible that decreasing the lock granularity like this will lead to
unforeseen latency issues. However, the additional work done under the new spin
lock is just a single list_add_tail() call, which appears to run in constant
time.
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