UBIFS performance

[Amit Kumar Sharma]

Hi Adrian

Really good information for us, In my understanding random 
read/write performance can not be greater then sequential , 
Am I right because I have seen in LFS on SSD  sequential and 
random performance are same , Please correct me if I am 
missing any scenario.we will measure performance using perf.

Thanks
Amit

----- Original Message ----- 
From: "Adrian Hunter" <ext-adrian.hunter at nokia.com>
To: "Brijesh Singh" <brij.singh at samsung.com>
Cc: <linux-mtd at lists.infradead.org>
Sent: Wednesday, November 26, 2008 5:19 PM
Subject: Re: UBIFS performance


> Brijesh Singh wrote:
>>   I am testing UBIFS and JFFS2 performance on OneNand 
>> with iozone utility.
>> Interestingly, random read / write performance are 
>> slightly better than
>> sequential read / write.
>> These results are consistent across multiple versions. 
>> And consistent with
>> all different record length sizes.
>>
>> Correct me if I am wrong, but shouldn't sequential 
>> read/write fair better
>> than random read/write? Is this expected behavior? If 
>> yes,why?
>
> For log-structured file systems on flash memory, there 
> should be little
> difference between sequential and random access.
>
> That is true for UBIFS, although sequential might be 
> slightly faster,
> because it is slightly more likely to find index nodes 
> already cached.
>
> We recently introduced a facility called bulk-read that 
> offers improved
> sequential read speed.  It has lower overhead and benefits 
> from OneNAND's
> read-while-load operation.
>
> We are thinking about something for writing in bigger 
> chunks that would
> benefit from OneNAND's write-while-program operation, but 
> that will be good
> for either random or sequential writes.
>
> With regard to iozone, you need to be aware that it hides 
> one of JFFS2's
> weaknesses which is how long it takes to open a file. 
> Unlike UBIFS and
> other file systems which just read the inode, JFFS2 has to 
> do lots of work
> putting all the file fragments together.  The bigger the 
> file, the longer
> it takes to open.  If you compare how long it takes to 
> open a file and
> read it, our experience is that UBIFS is faster than 
> JFFS2.  Whereas
> if you ignore the open time, JFFS2 is faster that UBIFS.
>
> In mtd-utils there is a simple performance test program 
> called perf
> which includes the open time in calculations.  It is in 
> the
> tests/fs-tests/simple directory.
>
> Also, if you want to exclude the effects of caching you 
> may want to use
> the -e and -U options for iozone.
>
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