scsi: lpfc: Mitigate high memory pre-allocation by SCSI-MQ
When SCSI-MQ is enabled, the SCSI-MQ layers will do pre-allocation of MQ
resources based on shost values set by the driver. In newer cases of the
driver, which attempts to set nr_hw_queues to the cpu count, the
multipliers become excessive, with a single shost having SCSI-MQ
pre-allocation reaching into the multiple GBytes range. NPIV, which
creates additional shosts, only multiply this overhead. On lower-memory
systems, this can exhaust system memory very quickly, resulting in a system
crash or failures in the driver or elsewhere due to low memory conditions.
After testing several scenarios, the situation can be mitigated by limiting
the value set in shost->nr_hw_queues to 4. Although the shost values were
changed, the driver still had per-cpu hardware queues of its own that
allowed parallelization per-cpu. Testing revealed that even with the
smallish number for nr_hw_queues for SCSI-MQ, performance levels remained
near maximum with the within-driver affiinitization.
A module parameter was created to allow the value set for the nr_hw_queues
to be tunable.
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
diff --git a/drivers/scsi/lpfc/lpfc_init.c b/drivers/scsi/lpfc/lpfc_init.c
index a7549ae..1ac98be 100644
--- a/drivers/scsi/lpfc/lpfc_init.c
+++ b/drivers/scsi/lpfc/lpfc_init.c
@@ -4309,10 +4309,12 @@ lpfc_create_port(struct lpfc_hba *phba, int instance, struct device *dev)
shost->max_cmd_len = 16;
if (phba->sli_rev == LPFC_SLI_REV4) {
- if (phba->cfg_fcp_io_sched == LPFC_FCP_SCHED_BY_HDWQ)
- shost->nr_hw_queues = phba->cfg_hdw_queue;
- else
- shost->nr_hw_queues = phba->sli4_hba.num_present_cpu;
+ if (!phba->cfg_fcp_mq_threshold ||
+ phba->cfg_fcp_mq_threshold > phba->cfg_hdw_queue)
+ phba->cfg_fcp_mq_threshold = phba->cfg_hdw_queue;
+
+ shost->nr_hw_queues = min_t(int, 2 * num_possible_nodes(),
+ phba->cfg_fcp_mq_threshold);
shost->dma_boundary =
phba->sli4_hba.pc_sli4_params.sge_supp_len-1;