Re: [PATCH 2/2] scsi: ufs: Use SYNCHRONIZE CACHE instead of FUA

[Bart Van Assche <bvanassche@acm.org>]

On 2/1/23 23:52, Adrian Hunter wrote:
> On 1/02/23 20:06, Bart Van Assche wrote:
>> UFS devices perform better when using SYNCHRONIZE CACHE command
>> instead of the FUA flag. Hence this patch.
> 
> It would be nice to get some clarification on what is
> going on for this case.
> 
> This includes with Data Reliability enabled?
> 
> In theory, WRITE+FUA should be at least as fast as
> WRITE+SYNCHRONIZE CACHE, right?
> 
> Do we have any explanation for why that would not
> be true?
> 
> In particular, is SYNCHRONIZE CACHE faster because
> it is not, in fact, providing Reliable Writes?
  Hi Adrian,

Setting the FUA bit in a WRITE command is functionally equivalent to 
submitting a WRITE command without FUA and submitting a SYNCHRONIZE 
CACHE command afterwards. For both sequences the storage device has to 
guarantee that the written data will survive a sudden power loss event.

It is not clear to me why WRITE + SYNCHRONIZE CACHE is faster than WRITE 
+ FUA. All I know is that this behavior has been observed for multiple 
UFS devices from multiple vendors. I hope that one of the UFS vendors 
can provide more information.

Bart.