Public bug reported:
[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 <chenxian...@hisilicon.com>
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.
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: dann frazier (dannf)
Status: In Progress
** Affects: linux (Ubuntu Bionic)
Importance: Undecided
Assignee: dann frazier (dannf)
Status: In Progress
** Attachment added: "fio"
https://bugs.launchpad.net/bugs/1794165/+attachment/5192579/+files/fio
** Also affects: linux (Ubuntu Bionic)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Bionic)
Status: New => In Progress
** Changed in: linux (Ubuntu Bionic)
Assignee: (unassigned) => dann frazier (dannf)
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https://bugs.launchpad.net/bugs/1794165
Title:
hisi_sas: Reduce unnecessary spin lock contention
Status in linux package in Ubuntu:
In Progress
Status in linux source package in Bionic:
In Progress
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 <chenxian...@hisilicon.com>
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.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1794165/+subscriptions
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