linux-kernel - Re: CONFIG_SCSI_MQ_DEFAULT cause slow direct write speed to usb stick

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Date:	Wed, 11 Feb 2015 14:02:37 +0100
From:	Andrej Gelenberg <andrej.gelenberg@....edu>
To:	Douglas Gilbert <dgilbert@...erlog.com>
Cc:	JBottomley@...allels.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@....de,
	martin.petersen@...cle.com, elliott@...com
Subject: Re: CONFIG_SCSI_MQ_DEFAULT cause slow direct write speed to usb
 stick

Hi,

my problem was, that write speed to the device is got really slow from
7 Mb/s to 250 Kb/s, so 16.76 Mb/sec is probably the speed limitation of
the uSD Card or is close to that. Do you activated blk-mq for scsi in
kernel config or in boot parameters?

Regards,
Andrej

On Tue, 10 Feb 2015 17:10:18 -0500
Douglas Gilbert <dgilbert@...erlog.com> wrote:

> Here is an example:
> 
> # ddpt if=/dev/sg1 bs=512 of=x.bin
> 1953792+0 records in
> 1953792+0 records out
> 1281 retries after EAGAIN error(s) during IO
> time to transfer data: 59.678788 secs at 16.76 MB/sec
> 
> That is not a bad transfer time but other utilities
> or drivers might dwell longer on those (nuisance) EAGAINs.
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