On 7/29/21 1:03 AM, Bean Huo wrote:
On Wed, 2021-07-21 at 20:34 -0700, Bart Van Assche wrote:
Using the UTRLCNR register involves two MMIO accesses in the hot path
while
using the doorbell register only involves a single MMIO access. Since
MMIO
accesses take time, do not use the UTRLCNR register. The spinlock
contention
on the SCSI host lock that is reintroduced by this patch will be
addressed
by a later patch.
This reverts commit 6f7151729647e58ac7c522081255fd0c07b38105.
Bart,
This commit is the key change in "Optimize host lock on TR send/compl
paths and utilize UTRLCNR"
https://patchwork.kernel.org/project/linux-scsi/cover/1621845419-14194-1-git-send-email-cang@xxxxxxxxxxxxxx/.
How did you compare the performance gain/loss after reverting this
commit?
Hi Bean,
I measured the performance impact of patches 11 and 12 combined. In a 4
KB read IOPS test I see that these two patches combined improve
performance by 1%. This illustrates that the two MMIO accesses of the
UTRLCNR register are slower than the single MMIO access of the doorbell
register.
Thanks,
Bart.
