Re: submit_bh leaves interrupts on upon return

[Jeff V. Merkey]

Jens Axboe wrote:

> On Thu, Jun 03 2004, Jeff V. Merkey wrote:
>  
>
> > Jens Axboe wrote:
> >
> >    
> >
> > > Submitting large numbers of buffer_heads from b_end_io is _nasty_, 2.4
> > > io scheduler runtime isn't exactly world champion and you are doing this
> > > at hard irq time. Not a good idea. Definitely not the true path to
> > > performance, unless you don't care about anything else in the system.
> > >
> > > At least in 2.6 you have a much faster io scheduler and the additionally
> > > large bio, so you wont spend nearly as much time there if you are
> > > clever. You still need process context, though, that hasn't changed.
> > >
> > >
> > >
> > >      
> > Sounds like I need to move to 2.6. I noticed the elevator is coalescing 
> > quite well, and since I am posting mostly continguous runs of sectors, 
> > what ends up at the adapter level would probably not change much much 
> > between 2.4 and 2.6 since I am maxing out the driver request queues as 
> > it is (255 pending requests of 32 scatter/gather elements of 256 sector 
> > runs). 2.6 might help but I suspect it will only help alleviate the 
> > submission overhead, and not make much difference on performance since 
> > the 3Ware card does have an upward limit on outstanding I/O requests.
> >    
>
> That's correct, it just helps you diminish the submission overhead by
> pushing down 256 sector entities in one go. So as long as you're io
> bound it won't give you better io performance, of course. If you are
> doing 400MiB/sec it should help you out, though.
>
>  
I'll give it a try n 2.6.

:-)

Jeff

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