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[SCSI] libfc: reduce hold time on SCSI host lock
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Introduce a new lock to protect the list of fc_fcp_pkt structs in libfc
instead of using the host lock.  This reduces the contention of this heavily
used lock, and I see up to a 25% performance gain in CPU bound small I/O
tests when scaling out across multiple quad-core CPUs.

The big win is in removing the host lock from the completion path
completely, as it does not need to be held around the call to scsi_done.

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
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Chris Leech authored and James Bottomley committed Dec 12, 2009
1 parent 5543c72 commit c1ecb90
Showing 1 changed file with 36 additions and 29 deletions.
65 changes: 36 additions & 29 deletions drivers/scsi/libfc/fc_fcp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -68,18 +68,20 @@ struct kmem_cache *scsi_pkt_cachep;

/**
* struct fc_fcp_internal - FCP layer internal data
* @scsi_pkt_pool: Memory pool to draw FCP packets from
* @scsi_pkt_pool: Memory pool to draw FCP packets from
* @scsi_queue_lock: Protects the scsi_pkt_queue
* @scsi_pkt_queue: Current FCP packets
* @last_can_queue_ramp_down_time: ramp down time
* @last_can_queue_ramp_up_time: ramp up time
* @max_can_queue: max can_queue size
*/
struct fc_fcp_internal {
mempool_t *scsi_pkt_pool;
struct list_head scsi_pkt_queue;
unsigned long last_can_queue_ramp_down_time;
unsigned long last_can_queue_ramp_up_time;
int max_can_queue;
mempool_t *scsi_pkt_pool;
spinlock_t scsi_queue_lock;
struct list_head scsi_pkt_queue;
unsigned long last_can_queue_ramp_down_time;
unsigned long last_can_queue_ramp_up_time;
int max_can_queue;
};

#define fc_get_scsi_internal(x) ((struct fc_fcp_internal *)(x)->scsi_priv)
Expand Down Expand Up @@ -410,12 +412,14 @@ static inline struct fc_frame *fc_fcp_frame_alloc(struct fc_lport *lport,
unsigned long flags;

fp = fc_frame_alloc(lport, len);
if (!fp) {
spin_lock_irqsave(lport->host->host_lock, flags);
fc_fcp_can_queue_ramp_down(lport);
spin_unlock_irqrestore(lport->host->host_lock, flags);
}
return fp;
if (likely(fp))
return fp;

/* error case */
spin_lock_irqsave(lport->host->host_lock, flags);
fc_fcp_can_queue_ramp_down(lport);
spin_unlock_irqrestore(lport->host->host_lock, flags);
return NULL;
}

/**
Expand Down Expand Up @@ -990,7 +994,7 @@ static void fc_fcp_cleanup_each_cmd(struct fc_lport *lport, unsigned int id,
struct scsi_cmnd *sc_cmd;
unsigned long flags;

spin_lock_irqsave(lport->host->host_lock, flags);
spin_lock_irqsave(&si->scsi_queue_lock, flags);
restart:
list_for_each_entry(fsp, &si->scsi_pkt_queue, list) {
sc_cmd = fsp->cmd;
Expand All @@ -1001,7 +1005,7 @@ static void fc_fcp_cleanup_each_cmd(struct fc_lport *lport, unsigned int id,
continue;

fc_fcp_pkt_hold(fsp);
spin_unlock_irqrestore(lport->host->host_lock, flags);
spin_unlock_irqrestore(&si->scsi_queue_lock, flags);

if (!fc_fcp_lock_pkt(fsp)) {
fc_fcp_cleanup_cmd(fsp, error);
Expand All @@ -1010,14 +1014,14 @@ static void fc_fcp_cleanup_each_cmd(struct fc_lport *lport, unsigned int id,
}

fc_fcp_pkt_release(fsp);
spin_lock_irqsave(lport->host->host_lock, flags);
spin_lock_irqsave(&si->scsi_queue_lock, flags);
/*
* while we dropped the lock multiple pkts could
* have been released, so we have to start over.
*/
goto restart;
}
spin_unlock_irqrestore(lport->host->host_lock, flags);
spin_unlock_irqrestore(&si->scsi_queue_lock, flags);
}

/**
Expand All @@ -1035,11 +1039,12 @@ static void fc_fcp_abort_io(struct fc_lport *lport)
* @fsp: The FCP packet to send
*
* Return: Zero for success and -1 for failure
* Locks: Called with the host lock and irqs disabled.
* Locks: Called without locks held
*/
static int fc_fcp_pkt_send(struct fc_lport *lport, struct fc_fcp_pkt *fsp)
{
struct fc_fcp_internal *si = fc_get_scsi_internal(lport);
unsigned long flags;
int rc;

fsp->cmd->SCp.ptr = (char *)fsp;
Expand All @@ -1049,13 +1054,16 @@ static int fc_fcp_pkt_send(struct fc_lport *lport, struct fc_fcp_pkt *fsp)
int_to_scsilun(fsp->cmd->device->lun,
(struct scsi_lun *)fsp->cdb_cmd.fc_lun);
memcpy(fsp->cdb_cmd.fc_cdb, fsp->cmd->cmnd, fsp->cmd->cmd_len);
list_add_tail(&fsp->list, &si->scsi_pkt_queue);

spin_unlock_irq(lport->host->host_lock);
spin_lock_irqsave(&si->scsi_queue_lock, flags);
list_add_tail(&fsp->list, &si->scsi_pkt_queue);
spin_unlock_irqrestore(&si->scsi_queue_lock, flags);
rc = lport->tt.fcp_cmd_send(lport, fsp, fc_fcp_recv);
spin_lock_irq(lport->host->host_lock);
if (rc)
if (unlikely(rc)) {
spin_lock_irqsave(&si->scsi_queue_lock, flags);
list_del(&fsp->list);
spin_unlock_irqrestore(&si->scsi_queue_lock, flags);
}

return rc;
}
Expand Down Expand Up @@ -1752,6 +1760,7 @@ int fc_queuecommand(struct scsi_cmnd *sc_cmd, void (*done)(struct scsi_cmnd *))
struct fcoe_dev_stats *stats;

lport = shost_priv(sc_cmd->device->host);
spin_unlock_irq(lport->host->host_lock);

rval = fc_remote_port_chkready(rport);
if (rval) {
Expand Down Expand Up @@ -1834,6 +1843,7 @@ int fc_queuecommand(struct scsi_cmnd *sc_cmd, void (*done)(struct scsi_cmnd *))
rc = SCSI_MLQUEUE_HOST_BUSY;
}
out:
spin_lock_irq(lport->host->host_lock);
return rc;
}
EXPORT_SYMBOL(fc_queuecommand);
Expand Down Expand Up @@ -1864,11 +1874,8 @@ static void fc_io_compl(struct fc_fcp_pkt *fsp)

lport = fsp->lp;
si = fc_get_scsi_internal(lport);
spin_lock_irqsave(lport->host->host_lock, flags);
if (!fsp->cmd) {
spin_unlock_irqrestore(lport->host->host_lock, flags);
if (!fsp->cmd)
return;
}

/*
* if can_queue ramp down is done then try can_queue ramp up
Expand All @@ -1880,10 +1887,8 @@ static void fc_io_compl(struct fc_fcp_pkt *fsp)
sc_cmd = fsp->cmd;
fsp->cmd = NULL;

if (!sc_cmd->SCp.ptr) {
spin_unlock_irqrestore(lport->host->host_lock, flags);
if (!sc_cmd->SCp.ptr)
return;
}

CMD_SCSI_STATUS(sc_cmd) = fsp->cdb_status;
switch (fsp->status_code) {
Expand Down Expand Up @@ -1945,10 +1950,11 @@ static void fc_io_compl(struct fc_fcp_pkt *fsp)
break;
}

spin_lock_irqsave(&si->scsi_queue_lock, flags);
list_del(&fsp->list);
spin_unlock_irqrestore(&si->scsi_queue_lock, flags);
sc_cmd->SCp.ptr = NULL;
sc_cmd->scsi_done(sc_cmd);
spin_unlock_irqrestore(lport->host->host_lock, flags);

/* release ref from initial allocation in queue command */
fc_fcp_pkt_release(fsp);
Expand Down Expand Up @@ -2216,6 +2222,7 @@ int fc_fcp_init(struct fc_lport *lport)
lport->scsi_priv = si;
si->max_can_queue = lport->host->can_queue;
INIT_LIST_HEAD(&si->scsi_pkt_queue);
spin_lock_init(&si->scsi_queue_lock);

si->scsi_pkt_pool = mempool_create_slab_pool(2, scsi_pkt_cachep);
if (!si->scsi_pkt_pool) {
Expand Down

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