[stgt] [PATCH 1/1] tgtd: Patch to add bsoflags options o tgtd.

[FUJITA Tomonori]

On Thu, 27 May 2010 17:10:43 -0300
Daniel Henrique Debonzi <debonzi at linux.vnet.ibm.com> wrote:

> FUJITA Tomonori wrote:
> > On Tue, 18 May 2010 16:21:00 -0300
> > Daniel Henrique Debonzi <debonzi at linux.vnet.ibm.com> wrote:
> > 
> >> One idea to solve it and don't make necessary to touch all backing 
> >> stores to avoid this issue is to create a new template like bs_rdrw_sync 
> >> O_SYNC and O_DIRECT flags on open, and don't have the options as this 
> >> patch does. This way I got want I am interested in and don't need to 
> >> involve all the other stuff. What are your thoughts about it?
> > 
> > Or a new option to touch only bs_rdrw.
> > 
> > However, I want to know why you want to use O_SYNC and O_DIRECT.
> > 
> > - what's the advantage of O_SYNC compared with the current approach
> > (sync_file after write)? notably faster?
> 
> We would like to be able to control those flags because for our case it 
> has better performance. Some tests done recently showed that we can get 
> good better results when using O_DIRECT than sync_file.

I see. Thanks for the explanation.

As we discussed, "--bsoflags" can't be applied to all the bs modes
equally (e.g. bs_aio can use only O_DIRECT). But I guess that creating
multiple options such as --bsoflags_rw, --bsoflags_aio, etc is too
overdoing.

I'll take the approach add only "--bsoflags". --bsoflags="async
direct" is not consistent with the other options. Let's use "," like
--bsoflags="async,direct".

I don't think that we need "none" or "async". Let's support "sync" and
"direct".

Can you please send the updated patch?


> > - why do you want to use O_DIRECT with bd_rdrw? bd_aio does aio with
> >   O_DIRECT? It's not enough for you?
> 
> AIO does not work with the kernel version we are using at moment.

Understood.
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