From: Jack Wang <xjtuwjp@gmail.com>
To: Alireza Haghdoost <alireza@cs.umn.edu>
Cc: linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org,
Jerry Fredin <jerry.fredin@netapp.com>
Subject: Re: Bypass block layer and Fill SCSI lower layer driver queue
Date: Wed, 18 Sep 2013 09:58:12 +0200 [thread overview]
Message-ID: <52395D14.6010103@gmail.com> (raw)
In-Reply-To: <CAB-428mCM-4c1hWaEJicB8Uz_4DCo7MsH-ZcXHrDkN=Wc5AhVA@mail.gmail.com>
On 09/18/2013 08:41 AM, Alireza Haghdoost wrote:
> Hi
>
> I am working on a high throughput and low latency application which
> does not tolerate block layer overhead to send IO request directly to
> fiber channel lower layer SCSI driver. I used to work with libaio but
> currently I am looking for a way to by pass the block layer and send
> SCSI commands from the application layer directly to the SCSI driver
> using /dev/sgX device and ioctl() system call.
>
> I have noticed that sending IO request through sg device even with
> nonblocking and direct IO flags is quite slow and does not fill up
> lower layer SCSI driver TCQ queue. i.e IO depth or
> /sys/block/sdX/in_flight is always ZERO. Therefore the application
> throughput is even lower that sending IO request through block layer
> with libaio and io_submit() system call. In both cases I used only one
> IO context (or fd) and single threaded.
>
Hi Alireza,
I think what you want is in_flight command scsi dispatch to low level
device.
I submit a simple patch to export device_busy
http://www.spinics.net/lists/linux-scsi/msg68697.html
I also notice fio sg engine will not fill queue properly, but haven't
look into deeper.
Cheers
Jack
> I have noticed that some well known benchmarking tools like fio does
> not support IO depth for sg devices as well. Therefore, I was
> wondering if it is feasible to bypass block layer and achieve higher
> throughput and lower latency (for sending IO request only).
>
>
> Any comment on my issue is highly appreciated.
>
>
> Thanks
> Alireza
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next prev parent reply other threads:[~2013-09-18 7:58 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-18 6:41 Bypass block layer and Fill SCSI lower layer driver queue Alireza Haghdoost
2013-09-18 7:58 ` Jack Wang [this message]
2013-09-18 14:07 ` Douglas Gilbert
2013-09-18 14:31 ` Boaz Harrosh
2013-09-27 6:06 ` Vladislav Bolkhovitin
2013-09-18 21:00 ` Nicholas A. Bellinger
2013-09-19 2:05 ` Alireza Haghdoost
2013-09-19 21:49 ` Nicholas A. Bellinger
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