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Commit c1ecb90a authored by Chris Leech's avatar Chris Leech Committed by James Bottomley
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[SCSI] libfc: reduce hold time on SCSI host lock 



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: default avatarChris Leech <christopher.leech@intel.com>
Signed-off-by: default avatarRobert Love <robert.w.love@intel.com>
Signed-off-by: default avatarJames Bottomley <James.Bottomley@suse.de>
parent 5543c72e

drivers/scsi/libfc/fc_fcp.c

+36 −29
Original line number Diff line number Diff line
@@ -69,6 +69,7 @@ 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_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
@@ -76,6 +77,7 @@ struct kmem_cache *scsi_pkt_cachep; 
 */

struct fc_fcp_internal {

	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;
@@ -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) {

	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 fp;

	return NULL;

}



/**
@@ -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;
@@ -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);
@@ -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);

}



/**
@@ -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;
@@ -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;

}
@@ -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) {
@@ -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);
@@ -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
@@ -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) {
@@ -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);
@@ -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) {