Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 2 Dec 2019 08:01:35 +0100
From:   Andrea Vai <andrea.vai@unipv.it>
To:     Bernd Schubert <bs_lists@aakef.fastmail.fm>
Cc:     Ming Lei <ming.lei@redhat.com>,
        "Schmid, Carsten" <Carsten_Schmid@mentor.com>,
        Finn Thain <fthain@telegraphics.com.au>,
        Damien Le Moal <Damien.LeMoal@wdc.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Jens Axboe <axboe@kernel.dk>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        USB list <linux-usb@vger.kernel.org>,
        SCSI development list <linux-scsi@vger.kernel.org>,
        Himanshu Madhani <himanshu.madhani@cavium.com>,
        Hannes Reinecke <hare@suse.com>,
        Omar Sandoval <osandov@fb.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Hans Holmberg <Hans.Holmberg@wdc.com>,
        Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: AW: Slow I/O on USB media after commit
 f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6
Message-ID: <20191202070135.GA4634@brian.unipv.it>
References: <0876e232feace900735ac90d27136288b54dafe1.camel@unipv.it>
 <20191126023253.GA24501@ming.t460p>
 <0598fe2754bf0717d81f7e72d3e9b3230c608cc6.camel@unipv.it>
 <alpine.LNX.2.21.1.1911271055200.8@nippy.intranet>
 <cb6e84781c4542229a3f31572cef19ab@SVR-IES-MBX-03.mgc.mentorg.com>
 <c1358b840b3a4971aa35a25d8495c2c8953403ea.camel@unipv.it>
 <20191128091712.GD15549@ming.t460p>
 <f82fd5129e3dcacae703a689be60b20a7fedadf6.camel@unipv.it>
 <20191129005734.GB1829@ming.t460p>
 <3c57bba1-831b-fc97-d5f7-e670f43fbbdc@aakef.fastmail.fm>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <3c57bba1-831b-fc97-d5f7-e670f43fbbdc@aakef.fastmail.fm>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 29/11/19 12:44:53, Bernd Schubert wrote:
> >> Trace attached. Produced by: start the trace script
> >> (with the pendrive already plugged), wait some seconds, run the test
> >> (1 trial, 1 GB), wait for the test to finish, stop the trace.
> >>
> >> The copy took 73 seconds, roughly as already seen before with the fast
> >> old kernel.
> > 
> > This trace shows a good write IO order because the writeback IOs are
> > queued to block layer serially from the 'cp' task and writeback wq.
> > 
> > However, writeback IO order is changed in current linus tree because
> > the IOs are queued to block layer concurrently from the 'cp' task
> > and writeback wq. It might be related with killing queue_congestion
> > by blk-mq.
> 
> What about using direct-io to ensure order is guaranteed? Pity that 'cp'
> doesn't seem to have an option for it. But dd should do the trick.
> Andrea, can you replace cp with a dd command (on the slow kernel)?
> 
> dd if=<path-to-src-file> of=<path-to-copy-on-flash-device> bs=1M
> oflag=direct

On the "new bad patched" kernel, this command take 68 seconds to complete (mean on 100 trials, with a narrow standard deviation), so perfectly
aligned with the cp command on the old fast good kernel.

Thanks, and bye
Andrea