From f8f91f3f3120b2168189100c588aeaf2ff5e9ac4 Mon Sep 17 00:00:00 2001 From: "Martin K. Petersen" Date: Fri, 14 Oct 2016 16:37:29 -0400 Subject: [PATCH] scsi: libfc: Revert "[SCSI] libfc: use offload EM instance again instead jumping to next EM" This 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. 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 Suggested-by: Curtis Taylor Tested-by: Laurence Oberman Signed-off-by: Laurence Oberman --- drivers/scsi/libfc/fc_exch.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c index 16ca31ad5ec0..dd95e2aece66 100644 --- a/drivers/scsi/libfc/fc_exch.c +++ b/drivers/scsi/libfc/fc_exch.c @@ -888,14 +888,19 @@ err: * EM is selected when a NULL match function pointer is encountered * or when a call to a match function returns true. */ -static inline struct fc_exch *fc_exch_alloc(struct fc_lport *lport, - struct fc_frame *fp) +static 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; } -- 2.30.2