Re: fsync() Performance Issue

[Manuel Krause <manuel.krause@mb.tu-ilmenau.de>]

On 05/07/2002 12:57 AM, Chris Mason wrote:

> On Mon, 2002-05-06 at 17:21, Hans Reiser wrote:
> 
>>>I'd rather not put it back in because it adds yet another corner case to
>>>maintain for all time.  Most of the fsync/O_SYNC bound applications are
>>>just given their own partition anyway, so most users that need data
>>>logging need it for every write.
>>>
>>>
>>Does mozilla's mail user agent use fsync?  Should I give it its own 
>>partition?  I bet it is fsync bound....;-)
>>
> 
> [ I took Wayne off the cc list, he's probably not horribly interested ]
> 
> Perhaps, but I'll also bet the fsync performance hit doesn't affect the
> performance of the system as a whole.  Remember that data=journal
> doesn't make the fsyncs fast, it just makes them faster.
> 
> 
>>Most persons using small fsyncs are using it because the person who 
>>wrote their application wrote it wrong.  What's more, many of the 
>>persons who wrote those applications cannot understand that they did it 
>>wrong even if you tell them (e.g. qmail author reportedly cannot 
>>understand, sendmail guys now understand but had Kirk McKusick on their 
>>staff and attending the meeting when I explained it to them so they are 
>>not very typical....).  
>>
>>In other words, handling stupidity is an important life skill, and we 
>>all need to excell at it.;-)
>>
> 
> A real strength to linux is the application designers can talk directly
> to their own personal bottlenecks.  Hopefully we reward those that hunt
> us down and spend the time convincing us their applications are worth
> tuning for.  They then proceed to beat the pants off their competition.
> 
> 
>>Tell me what your thoughts are on the following:
>>
>>If you ask randomly selected ReiserFS users (not the reiserfs-list, but 
>>the ones who would never send you an email....)  the following 
>>questions, what percentage will answer which choice?
>>
>>The filesystem you are using is named:
>>
>>a) the Performance Optimized SuSE FS
>>
>>b) NTFS
>>
>>c) FAT
>>
>>d) ext2
>>
>>e) ReiserFS
>>
> 
> I believe the ones that know what a filesystem is will answer ReiserFS,
> You might get a lot of ext2 answers, just because that's what a lot of
> people think the linux filesystem is.
> 
> 
>>If you want to change reiserfs to use data journaling you must do which:
>>
>>a) reinstall the reiserfs package using rpm
>>
>>b) modify /etc/fs.conf
>>
>>c) reinstall the operating system from scratch, and select different 
>>options during the install this time
>>
>>d) reformat your reiserfs partition using mkreiserfs
>>
>>e) none of the above
>>
>>f) all of the above except e)
>>
> 
> These people won't be admins of systems big enough for the difference to
> matter.  data journaling is targeted at people with so much load they
> would have to buy more hardware to make up for it.  The new option
> lowers the price to performance ratio, which is exactly what we want to
> do for sendmails, egeneras, lycos, etc.  If it takes my laptop 20ms to
> deliver a mail message, cutting the time down to 10ms just won't matter.
> 
> 
>>
>>What do you think the chances are that you can convince Hubert that 
>>every SuSE Enterprise Edition user should be asked at install time if 
>>they are going to use fsync a lot on each partition, and to use a 
>>different fstab setting if yes?
>>
> 
> Very little, I might tell them to buy the suse email server instead,
> since that would have the settings done right.  data=journal is just a
> small part of mail server tuning.
> 
> 
>>I know that you are an experienced sysadmin who was good at it.  Your 
>>intuition tells you that most sysadmins are like the ones you were 
>>willing to hire into your group at the university.  They aren't.
>>
>>Linux needs to be like a telephone.  You plug it in, push buttons, and 
>>talk.  It works well, but most folks don't know why.
>>
>>
> 
> Exactly.  I think there are 3 classes of users at play here.
> 
> 1) Those who don't understand and don't have enough load to notice.
> 2) Those who don't understand and do have enough load to notice.
> 3) Those who do understand and do have enough load to notice.
> 
> #2 will buy support from someone, and they should be able to configure
> the thing right.
> 
> #3 will find the docs and do it right themselves.
> 
> 
>>A moderate number of programs are small fsync bound for the simple 
>>reason that it is simpler to write them that way.    We need to cover 
>>over their simplistic designs.
>>
>>So, you have my sympathies Chris, because I believe you that it makes 
>>the code uglier and it won't be a joy to code and test.  I hope you also 
>>see that it should be done.
>>
> 
> Mostly, I feel this kind of tuning is a mistake right now.  The patch is
> young and there are so many places left to tweak...I'm still at the
> stage where much larger improvements are possible, and a better use of
> coding time.  Plus, it's monday and it's always more fun to debate than
> give in on mondays.
> 
> -chris
> 


Hi, Chris & Hans!

Don't think this somekind of destructive discussion would lead to 
anything useful for now, can you post a diff for 
2.4.19-pre7+latest-related-pending +compound-patch-from-ftp?

I'll try it and report if that leads to more security and/or less 
performance on my every day use with NS6 and so on if there is any.


Thanks,

Manuel