Commit 322617a0 authored by Koichiro Den's avatar Koichiro Den Committed by Jon Mason
Browse files

NTB: ntb_transport: Add 'tx_memcpy_offload' module option 



Some platforms (e.g. R-Car S4) do not gain from using a DMAC on TX path
in ntb_transport and end up CPU-bound on memcpy_toio(). Add a module
parameter 'tx_memcpy_offload' that moves the TX memcpy_toio() and
descriptor writes to a per-QP kernel thread. It is disabled by default.

This change also fixes a rare ordering hazard in ntb_tx_copy_callback(),
that was observed on R-Car S4 once throughput improved with the new
module parameter: the DONE flag write to the peer MW, which is WC
mapped, could be observed after the DB/MSI trigger. Both operations are
posted PCIe MWr (often via different OB iATUs), so WC buffering and
bridges may reorder visibility. Insert dma_mb() to enforce store->load
ordering and then read back hdr->flags to flush the posted write before
ringing the doorbell / issuing MSI.

While at it, update tx_index with WRITE_ONCE() at the earlier possible
location to make ntb_transport_tx_free_entry() robust.

Signed-off-by: default avatarKoichiro Den <den@valinux.co.jp>
Signed-off-by: default avatarJon Mason <jdmason@kudzu.us>
parent b36490b5

drivers/ntb/ntb_transport.c

+100 −4
Original line number Diff line number Diff line
@@ -54,12 +54,14 @@ 
#include <linux/errno.h>

#include <linux/export.h>

#include <linux/interrupt.h>

#include <linux/kthread.h>

#include <linux/module.h>

#include <linux/pci.h>

#include <linux/slab.h>

#include <linux/types.h>

#include <linux/uaccess.h>

#include <linux/mutex.h>

#include <linux/wait.h>

#include "linux/ntb.h"

#include "linux/ntb_transport.h"
@@ -100,6 +102,10 @@ module_param(use_msi, bool, 0644); 
MODULE_PARM_DESC(use_msi, "Use MSI interrupts instead of doorbells");

#endif



static bool tx_memcpy_offload;

module_param(tx_memcpy_offload, bool, 0644);

MODULE_PARM_DESC(tx_memcpy_offload, "Offload TX memcpy_toio() to a kernel thread");



static struct dentry *nt_debugfs_dir;



/* Only two-ports NTB devices are supported */
@@ -148,7 +154,9 @@ struct ntb_transport_qp { 
	void (*tx_handler)(struct ntb_transport_qp *qp, void *qp_data,

			   void *data, int len);

	struct list_head tx_free_q;

	struct list_head tx_offl_q;

	spinlock_t ntb_tx_free_q_lock;

	spinlock_t ntb_tx_offl_q_lock;

	void __iomem *tx_mw;

	phys_addr_t tx_mw_phys;

	size_t tx_mw_size;
@@ -199,6 +207,9 @@ struct ntb_transport_qp { 
	int msi_irq;

	struct ntb_msi_desc msi_desc;

	struct ntb_msi_desc peer_msi_desc;



	struct task_struct *tx_offload_thread;

	wait_queue_head_t tx_offload_wq;

};



struct ntb_transport_mw {
@@ -284,7 +295,13 @@ static int ntb_async_tx_submit(struct ntb_transport_qp *qp, 
static void ntb_memcpy_tx(struct ntb_queue_entry *entry, void __iomem *offset);

static int ntb_async_rx_submit(struct ntb_queue_entry *entry, void *offset);

static void ntb_memcpy_rx(struct ntb_queue_entry *entry, void *offset);

static int ntb_tx_memcpy_kthread(void *data);





static inline bool ntb_tx_offload_enabled(struct ntb_transport_qp *qp)

{

	return tx_memcpy_offload && qp && qp->tx_offload_thread;

}



static int ntb_transport_bus_match(struct device *dev,

				   const struct device_driver *drv)
@@ -1254,11 +1271,13 @@ static int ntb_transport_init_queue(struct ntb_transport_ctx *nt, 


	spin_lock_init(&qp->ntb_rx_q_lock);

	spin_lock_init(&qp->ntb_tx_free_q_lock);

	spin_lock_init(&qp->ntb_tx_offl_q_lock);



	INIT_LIST_HEAD(&qp->rx_post_q);

	INIT_LIST_HEAD(&qp->rx_pend_q);

	INIT_LIST_HEAD(&qp->rx_free_q);

	INIT_LIST_HEAD(&qp->tx_free_q);

	INIT_LIST_HEAD(&qp->tx_offl_q);



	tasklet_init(&qp->rxc_db_work, ntb_transport_rxc_db,

		     (unsigned long)qp);
@@ -1785,6 +1804,13 @@ static void ntb_tx_copy_callback(void *data, 


	iowrite32(entry->flags | DESC_DONE_FLAG, &hdr->flags);



	/*

	 * Make DONE flag visible before DB/MSI. WC + posted MWr may reorder

	 * across iATU/bridge (platform-dependent). Order and flush here.

	 */

	dma_mb();

	ioread32(&hdr->flags);



	if (qp->use_msi)

		ntb_msi_peer_trigger(qp->ndev, PIDX, &qp->peer_msi_desc);

	else
@@ -1805,7 +1831,7 @@ static void ntb_tx_copy_callback(void *data, 
	ntb_list_add(&qp->ntb_tx_free_q_lock, &entry->entry, &qp->tx_free_q);

}



static void ntb_memcpy_tx(struct ntb_queue_entry *entry, void __iomem *offset)

static void ntb_memcpy_tx_on_stack(struct ntb_queue_entry *entry, void __iomem *offset)

{

#ifdef ARCH_HAS_NOCACHE_UACCESS

	/*
@@ -1823,6 +1849,54 @@ static void ntb_memcpy_tx(struct ntb_queue_entry *entry, void __iomem *offset) 
	ntb_tx_copy_callback(entry, NULL);

}



static int ntb_tx_memcpy_kthread(void *data)

{

	struct ntb_transport_qp *qp = data;

	struct ntb_queue_entry *entry, *tmp;

	const int resched_nr = 64;

	LIST_HEAD(local_list);

	void __iomem *offset;

	int processed = 0;



	while (!kthread_should_stop()) {

		spin_lock_irq(&qp->ntb_tx_offl_q_lock);

		wait_event_interruptible_lock_irq_timeout(qp->tx_offload_wq,

				kthread_should_stop() ||

				!list_empty(&qp->tx_offl_q),

				qp->ntb_tx_offl_q_lock, 5*HZ);

		list_splice_tail_init(&qp->tx_offl_q, &local_list);

		spin_unlock_irq(&qp->ntb_tx_offl_q_lock);



		list_for_each_entry_safe(entry, tmp, &local_list, entry) {

			list_del(&entry->entry);

			offset = qp->tx_mw + qp->tx_max_frame * entry->tx_index;

			ntb_memcpy_tx_on_stack(entry, offset);

			if (++processed >= resched_nr) {

				cond_resched();

				processed = 0;

			}

		}

		cond_resched();

	}



	return 0;

}



static void ntb_memcpy_tx(struct ntb_queue_entry *entry, void __iomem *offset)

{

	struct ntb_transport_qp *qp = entry->qp;



	if (WARN_ON_ONCE(!qp))

		return;



	if (ntb_tx_offload_enabled(qp)) {

		ntb_list_add(&qp->ntb_tx_offl_q_lock, &entry->entry,

			     &qp->tx_offl_q);

		wake_up(&qp->tx_offload_wq);

	} else

		ntb_memcpy_tx_on_stack(entry, offset);

}



static int ntb_async_tx_submit(struct ntb_transport_qp *qp,

			       struct ntb_queue_entry *entry)

{
@@ -1895,6 +1969,9 @@ static void ntb_async_tx(struct ntb_transport_qp *qp, 
	hdr = offset + qp->tx_max_frame - sizeof(struct ntb_payload_header);

	entry->tx_hdr = hdr;



	WARN_ON_ONCE(!ntb_transport_tx_free_entry(qp));

	WRITE_ONCE(qp->tx_index, (qp->tx_index + 1) % qp->tx_max_entry);



	iowrite32(entry->len, &hdr->len);

	iowrite32((u32)qp->tx_pkts, &hdr->ver);
@@ -1935,9 +2012,6 @@ static int ntb_process_tx(struct ntb_transport_qp *qp, 


	ntb_async_tx(qp, entry);



	qp->tx_index++;

	qp->tx_index %= qp->tx_max_entry;



	qp->tx_pkts++;



	return 0;
@@ -2034,6 +2108,20 @@ ntb_transport_create_queue(void *data, struct device *client_dev, 
	qp->tx_handler = handlers->tx_handler;

	qp->event_handler = handlers->event_handler;



	init_waitqueue_head(&qp->tx_offload_wq);

	if (tx_memcpy_offload) {

		qp->tx_offload_thread = kthread_run(ntb_tx_memcpy_kthread, qp,

						    "ntb-txcpy/%s/%u",

						    pci_name(ndev->pdev), qp->qp_num);

		if (IS_ERR(qp->tx_offload_thread)) {

			dev_warn(&nt->ndev->dev,

				 "tx memcpy offload thread creation failed: %ld; falling back to inline copy\n",

				 PTR_ERR(qp->tx_offload_thread));

			qp->tx_offload_thread = NULL;

		}

	} else

		qp->tx_offload_thread = NULL;



	dma_cap_zero(dma_mask);

	dma_cap_set(DMA_MEMCPY, dma_mask);
@@ -2141,6 +2229,11 @@ void ntb_transport_free_queue(struct ntb_transport_qp *qp) 


	qp->active = false;



	if (qp->tx_offload_thread) {

		kthread_stop(qp->tx_offload_thread);

		qp->tx_offload_thread = NULL;

	}



	if (qp->tx_dma_chan) {

		struct dma_chan *chan = qp->tx_dma_chan;

		/* Putting the dma_chan to NULL will force any new traffic to be
@@ -2204,6 +2297,9 @@ void ntb_transport_free_queue(struct ntb_transport_qp *qp) 
	while ((entry = ntb_list_rm(&qp->ntb_tx_free_q_lock, &qp->tx_free_q)))

		kfree(entry);



	while ((entry = ntb_list_rm(&qp->ntb_tx_offl_q_lock, &qp->tx_offl_q)))

		kfree(entry);



	qp->transport->qp_bitmap_free |= qp_bit;



	dev_info(&pdev->dev, "NTB Transport QP %d freed\n", qp->qp_num);