Re: submit_bh leaves interrupts on upon return

[Jeff V. Merkey]

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.

Jeff

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