On Tue, 28 Mar 2017 10:32:19 +0300
Tariq Toukan [off-list ref] wrote:

On 27/03/2017 4:32 PM, Mel Gorman wrote:

quoted

On Mon, Mar 27, 2017 at 02:39:47PM +0200, Jesper Dangaard Brouer wrote:  

quoted

On Mon, 27 Mar 2017 10:55:14 +0200
Jesper Dangaard Brouer [off-list ref] wrote:
 

quoted

A possible solution, would be use the local_bh_{disable,enable} instead
of the {preempt_disable,enable} calls.  But it is slower, using numbers
from [1] (19 vs 11 cycles), thus the expected cycles saving is 38-19=19.

The problematic part of using local_bh_enable is that this adds a
softirq/bottom-halves rescheduling point (as it checks for pending
BHs).  Thus, this might affects real workloads.  

I implemented this solution in patch below... and tested it on mlx5 at
50G with manually disabled driver-page-recycling.  It works for me.

To Mel, that do you prefer... a partial-revert or something like this?
 

If Tariq confirms it works for him as well, this looks far safer patch  

Great.
I will test Jesper's patch today in the afternoon.

Good to hear :-)

quoted

than having a dedicate IRQ-safe queue. Your concern about the BH
scheduling point is valid but if it's proven to be a problem, there is
still the option of a partial revert.

I wanted to evaluate my own BH scheduling point concern, but I could
not, because I ran into a softirq acct regression (which I bisected
see[1]).  AFAIK this should not affect Tariq's multi-TCP-stream test
(netperf TCP stream testing works fine on my testlab).

[1] http://lkml.kernel.org/r/20170328101403.34a82fbf@redhat.com
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

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