[Crash-utility] [PATCH 1/2] Support for "dev -d|-D" options by parsing bitmap in blk-mq layer

[HAGIO KAZUHITO(萩尾 一仁)]

-----Original Message-----
> 	>       - Is it possible to use the new logic when blk-mq has sbitmap, even if
> 	>       a kernel has rq_dispatched and rq_completed?
> 	>
> 	>
> 	>
> 	> If we would like to replace the rq_dispatched/rq_completed with the sbitmap
> 	> to calculate the disk I/O statistics, that might be extra work.
> 	>
> 	> But anyway, if it's worth doing, we might consider doing it at the next stage.
> 	> What do  you think?
> 
> 	sorry, cannot get it.  I just mean this flow:
> 
> 	  if blk-mq uses sbitmap then
> 	      get_mq_diskio_from_hw_queues(q, &tmp);
> 	      return;
> 	  else if rq_dispatched/rq_completed exists then
> 	      ...
> 	      get_one_mctx_diskio(mctx_addr, &tmp);
> 
> 
> 
> It means that crash will preferentially use the sbitmap to calculate the disk I/O statistics
> since kernel started to introduce the sbitmap for the blk-mq feature.

Yes, right.

> 
> 
> 	What is the extra work?
> 
> 
> 
> The extra work is that: crash has to support parsing sbitmap on old kernel, and need to
> follow up the relevant kernel structure changes, it will make the implementation of the
> get_mq_diskio_from_hw_queues() become more complex. That is my concern.

Got it, thanks.

I thought that we wanted RHEL8 crash also fixed with this first series
as the bz is for RHEL8.  But ok, we can fix it later one by one.

Thanks,
Kazu