Commit 7ba2131a authored by Bart Van Assche's avatar Bart Van Assche Committed by Bart Van Assche
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FROMLIST: scsi: ufs: Disable zone write locking



From the UFSHCI 4.0 specification, about the legacy (single queue) mode:
"The host controller always process transfer requests in-order according
to the order submitted to the list. In case of multiple commands with
single doorbell register ringing (batch mode), The dispatch order for
these transfer requests by host controller will base on their index in
the List. A transfer request with lower index value will be executed
before a transfer request with higher index value."

From the UFSHCI 4.0 specification, about the MCQ mode:
"Command Submission
1. Host SW writes an Entry to SQ
2. Host SW updates SQ doorbell tail pointer

Command Processing
3. After fetching the Entry, Host Controller updates SQ doorbell head
   pointer
4. Host controller sends COMMAND UPIU to UFS device"

In other words, for both legacy and MCQ mode, UFS controllers are
required to forward commands to the UFS device in the order these
commands have been received from the host.

Notes:
- For legacy mode this is only correct if the host submits one
  command at a time. The UFS driver does this.
- Also in legacy mode, the command order is not preserved if
  auto-hibernation is enabled in the UFS controller. Hence, enable
  zone write locking if auto-hibernation is enabled.

This patch improves performance as follows on my test setup:
- With the mq-deadline scheduler: 2.5x more IOPS for small writes.
- When not using an I/O scheduler compared to using mq-deadline with
  zone locking: 4x more IOPS for small writes.

Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Avri Altman <avri.altman@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Change-Id: Ie569b09ed78ecb91af0a13f56992f075f8d1f07a
Signed-off-by: default avatarBart Van Assche <bvanassche@acm.org>
Bug: 234829282
Link: https://lore.kernel.org/linux-block/20230804154821.3232094-1-bvanassche@acm.org/T/#mbfe0e160cc8a47c16af598f1c0b3aeeb125d66de


Signed-off-by: default avatarBart Van Assche <bvanassche@google.com>
parent 4224108a
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