linux-kernel - RE: [PATCH] usb-storage: Optimize scan delay more precisely

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Message-ID:
 <TYVPR01MB10781C18C8177783D8DEF7E69903B2@TYVPR01MB10781.jpnprd01.prod.outlook.com>
Date: Thu, 28 Mar 2024 02:52:35 +0000
From: Norihiko Hama <norihiko.hama@...salpine.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"usb-storage@...ts.one-eyed-alien.net"
	<usb-storage@...ts.one-eyed-alien.net>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb-storage: Optimize scan delay more precisely

> > On Wed, Mar 27, 2024 at 07:39:55AM +0000, Norihiko Hama wrote:
> > > > > Sorry, but module parameters are from the 1990's, we will not go back to that if at all possible as it's not easy to maintain and will not work properly for multiple devices.
> > > > >
> > > > > I can understand wanting something between 1 and 0 seconds, but adding yet-another-option isn't probably the best way, sorry.
> > > > 1 second does not meet with performance requirement.
> > >
> > > Who is requiring such a performance requirement?  The USB specification?
> > > Or something else?
> > This is our customer requirement.
>
> If it is impossible to do, why are they making you do it?  :)

It's possible to do because we've changed code to minimize delay by ourselves,
Then no issue observed when we configured delay to 100 msec as far as we have tested.
The background for the requirement, it's important for end user how quickly access to USB drive when it's connected.
Of course there are a lot of overhead to do that but that's why we would like to have a chance to minimize such a constant long delay.

> > I know we have multiple devices with delay_use=0, but then it's recovered and detected by reset after 30s timeout, that is too long than 1 sec.
>
> So how do you know that making this smaller will help?  There are many many odd and broken devices out there that take a long time to spin up before they are able to be > accessed.  That's what that option is there for, if you "know" you don't need to wait, you don't have to wait.
> Otherwise you HAVE to wait as you do not know how long things take.

As previous my comment, we've changed code to minimize delay by ourselves,
Then no issue observed when we configured delay to 100 msec as far as we have tested.
Sorry, we have no theoretical proof but I think it's same situation with current 1 sec delay.
So we want to have a chance to change such a constant delay.