On 10/13/2016 02:43 PM, Laurence Oberman wrote:
> 
> 
> Hello
> 
> This patch reverts commit 3e22760d4db6fd89e0be46c3d132390a251da9c6.
> 
> This revert came about because of efforts by Ewan Milne, Curtis Taylor and I.
> In researching this issue, significant performance issues were seen on large 
> CPU count 
> systems using the software FCOE stack.
> Hannes also weighed in.
> 
> The same was not apparent on much smaller low count CPU systems.
> The behavior introduced by commit 3e22760d4db6fd89e0be46c3d132390a251da9c6 
> lands sup with large
> count CPU systems seeing continual blk_requeue_request() calls due to 
> ML_QUEUE_HOST_BUSY.
> 
> From Ewan:
> 
> fc_exch_alloc() used to try all the available exchange managers in the
> list for an available exchange id, but this was changed in 2010 so that
> if the first matched exchange manager couldn't allocate one, it fails
> and we end up returning host busy.  This was due to commit:
> 
> Setting the ddp_min module parameter to fcoe to 128MB prevents the ->match
> function from permitting the use of the offload exchange manager for the 
> frame,
> and we no longer see the problem with host busy status, since it uses the
> larger non-offloaded pool.
> 
> Reverting commit 3e22760d4db6fd89e0be46c3d132390a251da9c6 was tested to also
> prevent the host busy issue due to failing allocations.
> 
> Suggested-by: Ewan Milne <emi...@redhat.com>
> Suggested-by: Curtis Taylor <c...@us.ibm.com>
> Tested-by: Laurence Oberman <lober...@redhat.com>
> Signed-off-by: Laurence Oberman <lober...@redhat.com>
> 
> diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c
> index e72673b..d5c4048 100644
> --- a/drivers/scsi/libfc/fc_exch.c
> +++ b/drivers/scsi/libfc/fc_exch.c
> @@ -892,10 +892,15 @@ static inline struct fc_exch *fc_exch_alloc(struct 
> fc_lport *lport,
>                                           struct fc_frame *fp)
>  {
>       struct fc_exch_mgr_anchor *ema;
> +     struct fc_exch *ep;
>  
> -     list_for_each_entry(ema, &lport->ema_list, ema_list)
> -             if (!ema->match || ema->match(fp))
> -                     return fc_exch_em_alloc(lport, ema->mp);
> +     list_for_each_entry(ema, &lport->ema_list, ema_list) {
> +             if (!ema->match || ema->match(fp)) {
> +                     ep = fc_exch_em_alloc(lport, ema->mp);
> +                     if (ep)
> +                             return ep;
> +             }
> +     }
>       return NULL;
>  }
> 
Reviewed-by: Hannes Reinecke <h...@suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Teamlead Storage & Networking
h...@suse.de                                   +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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