Re: submit_bh leaves interrupts on upon return

["Jeff V. Merkey" <jmerkey@drdos.com>]

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