From: Jens Axboe <axboe@kernel.dk>
To: Alireza Haghdoost <haghdoost@gmail.com>
Cc: fio@vger.kernel.org
Subject: Re: Workload Request Size issue
Date: Mon, 18 Feb 2013 09:04:53 +0100 [thread overview]
Message-ID: <20130218080453.GB6003@kernel.dk> (raw)
In-Reply-To: <CAB-428nhEKv83KVm03NMGgSEbHGTjGAgv8Prkt7xFRmznzJfGA@mail.gmail.com>
On Sat, Feb 16 2013, Alireza Haghdoost wrote:
> Hello,
>
> I am using fio to generate a simple sequential workload with request
> size of 128K with following job file but I can observe the generated
> IO request size is 4K, I was wondering who is responsible in block
> layer to shrink the fio requests granularity from 128K to 4K ? :
>
>
> 1 ; -- start job file --
> 2 [global]
> 3 rw=write
> 4 size=128M
> 5
> 6 [job1]
> 7 ioengine=libaio
> 8 iodepth=512
> 9 bs=128k
> 10 direct=1
> 11 numjobs=1
> 12 filename=/dev/sde
> 13 ; -- end job file --
>
>
> The blktrace shows that the request sizes are all 4KB (8 sector), here
> is a peace of output trace that collected while fio is running.
>
> 21 8,64 5 21 0.000031322 29848 I W 32 + 8 [fio]
> 22 8,64 5 22 0.000031868 29848 Q WS 40 + 8 [fio]
> 23 8,64 5 23 0.000032181 29848 G WS 40 + 8 [fio]
> 24 8,64 5 24 0.000032352 29848 I W 40 + 8 [fio]
> 25 8,64 5 25 0.000032826 29848 Q WS 48 + 8 [fio]
> 26 8,64 5 26 0.000033145 29848 G WS 48 + 8 [fio]
> 27 8,64 5 27 0.000033310 29848 I W 48 + 8 [fio]
> 28 8,64 5 28 0.000033781 29848 Q WS 56 + 8 [fio]
> 29 8,64 5 29 0.000034045 29848 G WS 56 + 8 [fio]
> 30 8,64 5 30 0.000034227 29848 I W 56 + 8 [fio]
> 31 8,64 5 31 0.000034498 29848 D W 32 + 8 [fio]
> 32 8,64 5 32 0.000036314 29848 D W 40 + 8 [fio]
> 33 8,64 5 33 0.000038032 29848 D W 48 + 8 [fio]
What kernel are you using? For a proper setup, the above fio job should
go down to the hardware as 128KB sized requests. Depending on the kernel
and driver, there might be timing issues that cause it to not get
properly coalesced in the scheduler, however.
--
Jens Axboe
next prev parent reply other threads:[~2013-02-18 8:06 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-16 16:19 Workload Request Size issue Alireza Haghdoost
2013-02-18 8:04 ` Jens Axboe [this message]
2013-02-19 2:49 ` Alireza Haghdoost
2013-02-19 12:54 ` Jens Axboe
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