linux-kernel - RE: [PATCH v2] scsi: ufs: Allow RTT negotiation

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Date: Fri, 10 May 2024 04:00:09 +0000
From: Avri Altman <Avri.Altman@....com>
To: Bean Huo <huobean@...il.com>, "Martin K . Petersen"
	<martin.petersen@...cle.com>
CC: Bart Van Assche <bvanassche@....org>, Bean Huo <beanhuo@...ron.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] scsi: ufs: Allow RTT negotiation

> On Fri, 2024-05-03 at 14:34 +0300, Avri Altman wrote:
> > UFS4.0, and specifically gear 5 changes this, and requires the device
> > to be more attentive.  This doesn't come free - the device has to
> > allocate more resources to that end, but the sequential write
> > performance improvement is significant. Early measurements shows 25%
> > gain when moving from rtt 2 to 9. Therefore, set bMaxNumOfRTT to be
> > min(bDeviceRTTCap, NORTT) as UFSHCI expects.
> >
> > Signed-off-by: Avri Altman <avri.altman@....com>
> 
> 
> Avri,
> 
> I was still curious about this 25% gain, so I will take a look. It would be great if
> you could share more information about this.
Thanks.
Those are just from early measurements.
But it perfectly makes sense to me: The rtt upiu works like Toyota's kanban cards.
And in gear 5 - there isn't enough cards...

Thanks,
Avri
> 
> 
> 
> Reviewed-by: Bean Huo <beanhuo@...ron.com>
> 
>