tree 8a3e23cc8c248bd7ea06c2920729d5e82ce0e886
parent 24920c8a6358bf5532f1336b990b1c0fe2b599ee
author Matthew Wilcox <matthew@wil.cx> 1215350600 -0400
committer Jeff Garzik <jgarzik@redhat.com> 1216065574 -0400

AHCI: Remove an unnecessary flush from ahci_qc_issue

In an I/O heavy workload (IOZone), ahci_qc_issue is the second-highest
consumer of CPU cycles.  Removing the flush gets us approximately 10%
bandwidth improvement.  I believe this to be because the CPU can start
queueing the next request instead of waiting for the readl() to flush the
writes to the device.  The flush isn't necessary because we're using a
'queue' metaphor; we don't guarantee the command has got to the device,
nor do we need to guarantee the command has got to the controller.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>