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hpsa: optimize cmd_alloc function by remembering last allocation

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Empirically, this improves performance slightly (~2% max IOPS) by
allowing cmd_alloc to remember where it left off searching for
free commands between calls instead of always starting its search
at command 0.

Reviewed-by: Scott Teel <scott.teel@pmcs.com>
Signed-off-by: Robert Elliott <elliott@hp.com>
Signed-off-by: Don Brace <don.brace@pmcs.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Robert Elliott
2015-01-23 16:43:41 -06:00
committed by James Bottomley
parent 281a7fd03e
commit 33811026a0
2 changed files with 6 additions and 2 deletions
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drivers/scsi/hpsa.c
+5 -2
View File
@@ -4649,9 +4649,10 @@ static struct CommandList *cmd_alloc(struct ctlr_info *h)
union u64bit temp64; union u64bit temp64;
dma_addr_t cmd_dma_handle, err_dma_handle; dma_addr_t cmd_dma_handle, err_dma_handle;
int refcount; int refcount;
unsigned long offset = 0; unsigned long offset;
/* There is some *extremely* small but non-zero chance that that /*
* There is some *extremely* small but non-zero chance that that
* multiple threads could get in here, and one thread could * multiple threads could get in here, and one thread could
* be scanning through the list of bits looking for a free * be scanning through the list of bits looking for a free
* one, but the free ones are always behind him, and other * one, but the free ones are always behind him, and other
@@ -4662,6 +4663,7 @@ static struct CommandList *cmd_alloc(struct ctlr_info *h)
* infrequently as to be indistinguishable from never. * infrequently as to be indistinguishable from never.
*/ */
offset = h->last_allocation; /* benignly racy */
for (;;) { for (;;) {
i = find_next_zero_bit(h->cmd_pool_bits, h->nr_cmds, offset); i = find_next_zero_bit(h->cmd_pool_bits, h->nr_cmds, offset);
if (unlikely(i == h->nr_cmds)) { if (unlikely(i == h->nr_cmds)) {
@@ -4679,6 +4681,7 @@ static struct CommandList *cmd_alloc(struct ctlr_info *h)
h->cmd_pool_bits + (i / BITS_PER_LONG)); h->cmd_pool_bits + (i / BITS_PER_LONG));
break; /* it's ours now. */ break; /* it's ours now. */
} }
h->last_allocation = i; /* benignly racy */
/* Zero out all of commandlist except the last field, refcount */ /* Zero out all of commandlist except the last field, refcount */
memset(c, 0, offsetof(struct CommandList, refcount)); memset(c, 0, offsetof(struct CommandList, refcount));
drivers/scsi/hpsa.h
+1
View File
@@ -133,6 +133,7 @@ struct ctlr_info {
struct CfgTable __iomem *cfgtable; struct CfgTable __iomem *cfgtable;
int interrupts_enabled; int interrupts_enabled;
int max_commands; int max_commands;
int last_allocation;
atomic_t commands_outstanding; atomic_t commands_outstanding;
# define PERF_MODE_INT 0 # define PERF_MODE_INT 0
# define DOORBELL_INT 1 # define DOORBELL_INT 1