linux-kernel - Re: [PATCH 4.19 114/149] UAS: Revert commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments")

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Message-ID: <20191105163805.GB2760793@kroah.com>
Date:   Tue, 5 Nov 2019 17:38:05 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 4.19 114/149] UAS: Revert commit 3ae62a42090f ("UAS: fix
 alignment of scatter/gather segments")

On Tue, Nov 05, 2019 at 04:41:07PM +0100, Oliver Neukum wrote:
> Am Dienstag, den 05.11.2019, 10:09 -0500 schrieb Alan Stern:
> > On Tue, 5 Nov 2019, Oliver Neukum wrote:
> > 
> > > Am Montag, den 04.11.2019, 22:45 +0100 schrieb Greg Kroah-Hartman:
> > > >         Since commit ea44d190764b ("usbip: Implement SG support to
> > > >         vhci-hcd and stub driver") was merged, the USB/IP driver can
> > > >         also handle SG.
> > > 
> > > Hi,
> > > 
> > > same story as 4.4.x
> > 
> > I'm not sure about uas, but it was reported just yesterday that the 
> > corresponding commit for usb-storage caused a 30% speed degradation:
> > 
> > 	https://marc.info/?l=linux-usb&m=157293660212040&w=2
> > 
> > Given this information, perhaps you will decide that the revert is 
> > worthwhile.
> 
> Damned if I do, damned if I do not.
> Check for usbip and special case it?

We should be able to do that in the host controller driver for usbip,
right?  What is the symptom if you use a UAS device with usbip and this
commit?

thanks,

greg k-h