Re: [RFC] [PATCH] 2.5.35 patch for making DIO async--performance numbers

[Badari Pulavarty]

Andrew,

> 
> Thanks.  Note that the old code (which seems to be a tiny bit faster,
> and used less CPU as well) has a significantly higher context switch
> rate.  At a guess I'd say that it is more efficient at getting userspace
> up and running in response to IO completion.
> 

I my patch, I removed bio_list. So, I do all the processing of "bio"
in end_io() function, instead of postpone it to waiter. Do you think
this matters ? 

> I'd say it's only likely to affect these huge linear IOs.  Once you get
> into real workloads which are seeking and merging then a bit of latency
> here or there would just be soaked up by other system activity.
> 
> Ah.  The current direct-io.c uses wake_up_process(), not waitqueues.
> So the aio version has to wear the waitqueue cost.  If you're using the
> -mm patch I'd suggest that you convert aio.c to prepare_to_wait/finish_wait.
> The waitqueue/wakeup costs on your 8-ways seem to be very high.

Ok !! I still use wake_up_process() for the sync case.
I will try to use waitqueues and see.

Thanks,
Badari