linux-kernel - Re: read performance is too low compared to write

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Date:	Mon, 17 Nov 2014 02:14:52 +0530
From:	Jagan Teki <jagannadh.teki@...il.com>
To:	Roger Heflin <rogerheflin@...il.com>
Cc:	Tejun Heo <tj@...nel.org>, davem <davem@...emloft.net>,
	linux-ide <linux-ide@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: read performance is too low compared to write - /dev/sda1

On 14 November 2014 19:22, Roger Heflin <rogerheflin@...il.com> wrote:
> What kind of underlying disk is it?

GEN3 Sata link, SSD from Samsung.

>
> On Fri, Nov 14, 2014 at 7:36 AM, Jagan Teki <jagannadh.teki@...il.com> wrote:
>> On 14 November 2014 18:50, Roger Heflin <rogerheflin@...il.com> wrote:
>>> If you are robocoping small files you will hit other limits.
>>>
>>> Best I have seen with small files is around 30 files/second, and that
>>> involves multiple copies going on.   Remember with a small files there
>>> are several reads and writes that need to be done to complete a create
>>> of a small file and each of these take time.    30 files/second ~ 30ms
>>> per file, not that bad considering that on a real spinning disk a
>>> single read/write op is 5-10ms, and creating the file entry, copying
>>> data and closing the file takes several operations (at least create
>>> file entry, write small amount of data, update file entry
>>> date/time/info).     If the write in the middle is not a significant
>>> amount of data, the 2 extra ops are what hurts.
>>>
>>
>> But, I tried 4gb and 1gb files both got a similar numbers.
>>
>>> On Fri, Nov 14, 2014 at 6:55 AM, Jagan Teki <jagannadh.teki@...il.com> wrote:
>>>> Hi,
>>>>
>>>> I'm doing a performance testing on my bench ARM box.
>>>>
>>>> 1. dd test: I have validate the read and write by mounting /dev/sda1
>>>> with ext4 filesystem,
>>>>     able to get the good performance numbers where read is high
>>>> compared to write
>>>>
>>>> 2.  robocopy test:
>>>>      - mkfs.ext4 /dev/sda1
>>>>      - mount /dev/sda1 /media/disk
>>>>      - << configured samba >>
>>>>      - Mapped the /media/disk on windows
>>>>      - login on the mapped driver in windows
>>>>      - did a robocopy test, where write got 84MBps and read 14MBps
>>>>
>>>> read performance is too slow when compared to write in robocopy case.
>>>> Can anyone help me out, how to debug this further.
>>
>> thanks!
>> --
>> Jagan.



-- 
Jagan.
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