[PATCH 2/2] cxlflash: Move to exponential back-off when cmd_room is not available

[Matthew R. Ochs]

> On Mar 23, 2016, at 2:50 PM, Uma Krishnan <ukrishn at linux.vnet.ibm.com> wrote:
> 
> From: "Manoj N. Kumar" <manoj at linux.vnet.ibm.com>
> 
> While profiling the cxlflash_queuecommand() path under a heavy load it
> was found that number of retries to find cmd_room was fairly high.
> 
> There are two problems with the current back-off:
> a) It starts with a udelay of 0
> b) It backs-off linearly
> 
> Tried several approaches (a higher multiple 10*n, 100*n, as well as n^2,
> 2^n) and found that the exponential back-off(2^n) approach had the least
> overall cost. Cost as being defined as overall time spent waiting.
> 
> The fix is to change the linear back-off to an exponential back-off.
> This solution also takes care of the problem with the initial
> delay (starts with 1 usec).
> 
> Signed-off-by: Manoj N. Kumar <manoj at linux.vnet.ibm.com>

Acked-by: Matthew R. Ochs <mrochs at linux.vnet.ibm.com>