Re: [PATCH] IB/ehca: Serialize HCA-related hCalls on POWER5

Hi, guys,

We're taking this to the firmware architects at the moment, but they're 

not 

very fond of the idea of reporting the absence of bugs through 

capability 

flags, as this could quickly lead to the exhaustion of flag bits. We'll 

let 

the discussion stew for a bit, but if we don't get this flag, we'll have 

to 

resort to the CPU features.

The architects have spoken, and we're getting a capability flag for this. 
I'll repost my patch with new autodetection code that doesn't involve 
checking the processor version.
 

quoted

 > Regarding the performance problem, have you checked whether 

converting all

quoted

 > your spin_lock_irqsave to spin_lock/spin_lock_irq improves your 

performance

quoted

 > on the older machines? Maybe it's already fast enough that way.

It does seem that the only places that the hcall_lock is taken also
use msleep, so they must always be in process context.  So you can
safely just use spin_lock(), right?

As Arnd said, there are hCalls that will never return H_LONG_BUSY_*, 

such as 

H_QUERY_PORT and chums, so they will never sleep. The surrounding 

functions, 

though, are not prepared to be called from interrupt context (GFP_KERNEL 

comes

to mind), so I agree that a simple spin_lock() will suffice. Thanks, 

Arnd, for

pointing this out.

As I pointed out in my earlier mail, there's still an issue with 
map_phys_fmr possibly sleeping. Let's keep the irqsave for the time being 
and revisit this part once we find a solution to map_phys_fmr.

Regards,
  Joachim