In a high-IOPS workload, mpt2sas_base_get_smid_scsiio shows up in the top 20 cache misses. This is because the data structure used for allocating SMIDs is cache unfriendly; freed SMIDs are placed on the tail of the list, guaranteeing a cache miss by the time we allocate it again. By placing the freed SMID at the head of the list, we increase the likelihood of it being cache-hot when it's used again. Signed-off-by: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx> diff --git a/drivers/scsi/mpt2sas/mpt2sas_base.c b/drivers/scsi/mpt2sas/mpt2sas_base.c index 9ead039..1137cc9 100644 --- a/drivers/scsi/mpt2sas/mpt2sas_base.c +++ b/drivers/scsi/mpt2sas/mpt2sas_base.c @@ -1501,13 +1501,13 @@ mpt2sas_base_free_smid(struct MPT2SAS_ADAPTER *ioc, u16 smid) /* hi-priority */ i = smid - ioc->hi_priority_smid; ioc->hpr_lookup[i].cb_idx = 0xFF; - list_add_tail(&ioc->hpr_lookup[i].tracker_list, + list_add(&ioc->hpr_lookup[i].tracker_list, &ioc->hpr_free_list); } else { /* internal queue */ i = smid - ioc->internal_smid; ioc->internal_lookup[i].cb_idx = 0xFF; - list_add_tail(&ioc->internal_lookup[i].tracker_list, + list_add(&ioc->internal_lookup[i].tracker_list, &ioc->internal_free_list); } spin_unlock_irqrestore(&ioc->scsi_lookup_lock, flags); @@ -1520,14 +1520,13 @@ mpt2sas_base_free_smid(struct MPT2SAS_ADAPTER *ioc, u16 smid) list_for_each_entry_safe(chain_req, next, &ioc->scsi_lookup[i].chain_list, tracker_list) { list_del_init(&chain_req->tracker_list); - list_add_tail(&chain_req->tracker_list, + list_add(&chain_req->tracker_list, &ioc->free_chain_list); } } ioc->scsi_lookup[i].cb_idx = 0xFF; ioc->scsi_lookup[i].scmd = NULL; - list_add_tail(&ioc->scsi_lookup[i].tracker_list, - &ioc->free_list); + list_add(&ioc->scsi_lookup[i].tracker_list, &ioc->free_list); spin_unlock_irqrestore(&ioc->scsi_lookup_lock, flags); /* -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html