SRP I/O with small block sizes causes a high CPU load. Processing IB
completions on the context of a kernel thread instead of in interrupt context
allows to process up to 25% more I/O operations per second. This patch does
add a kernel parameter 'thread' that allows to specify whether to process IB
completions in interrupt context or in kernel thread context. Also, the IB
receive notification processing loop is rewritten as proposed earlier by Ralph
Campbell (see also https://patchwork.kernel.org/patch/89426/). As the
measurement results below show, rewriting the IB receive notification
processing loop did not have a measurable impact on performance. Processing
IB receive notifications in thread context however does have a measurable
impact: workloads with I/O depth one are processed at most 10% slower and
workloads with larger I/O depths are processed up to 25% faster.
block size number of IOPS IOPS IOPS
in bytes threads without with with
($bs) ($numjobs) this patch thread=n thread=y
512 1 25,400 25,400 23,100
512 128 122,000 122,000 153,000
4096 1 25,000 25,000 22,700
4096 128 122,000 121,000 157,000
65536 1 14,300 14,400 13,600
65536 4 36,700 36,700 36,600
524288 1 3,470 3,430 3,420
524288 4 5,020 5,020 4,990
performance test used to gather the above results:
fio --bs=${bs} --ioengine=sg --buffered=0 --size=128M --rw=read \
--thread --numjobs=${numjobs} --loops=100 --group_reporting \
--gtod_reduce=1 --name=${dev} --filename=${dev}
other ib_srp kernel module parameters: srp_sg_tablesize=128
SRP target settings: storage type NULLIO; SCSI queue depth 128.
IB HCA type: QDR.
Signed-off-by: Bart Van Assche <bvanass...@acm.org>
Cc: Roland Dreier <rola...@cisco.com>
Cc: David Dillow <d...@thedillows.org>
Cc: Ralph Campbell <ralph.campb...@qlogic.com>
diff --git a/drivers/infiniband/ulp/srp/ib_srp.c
b/drivers/infiniband/ulp/srp/ib_srp.c
index ed3f9eb..eebe870 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -1,5 +1,6 @@
/*
* Copyright (c) 2005 Cisco Systems. All rights reserved.
+ * Copyright (c) 2009-2010 Bart Van Assche <bvanass...@acm.org>.
*
* This software is available to you under a choice of one of two
* licenses. You may choose to be licensed under the terms of the GNU
@@ -38,6 +39,7 @@
#include <linux/parser.h>
#include <linux/random.h>
#include <linux/jiffies.h>
+#include <linux/kthread.h>
#include <asm/atomic.h>
@@ -66,6 +68,12 @@ module_param(srp_sg_tablesize, int, 0444);
MODULE_PARM_DESC(srp_sg_tablesize,
"Max number of gather/scatter entries per I/O (default is 12,
max 255)");
+static bool thread;
+module_param(thread, bool, 0444);
+MODULE_PARM_DESC(thread,
+ "Whether to process IB completions in interrupt context
(false) or"
+ " kernel thread context (true)");
+
static int topspin_workarounds = 1;
module_param(topspin_workarounds, int, 0444);
@@ -81,6 +89,8 @@ MODULE_PARM_DESC(mellanox_workarounds,
static void srp_add_one(struct ib_device *device);
static void srp_remove_one(struct ib_device *device);
static void srp_recv_completion(struct ib_cq *cq, void *target_ptr);
+static void srp_notify_recv_thread(struct ib_cq *cq, void *target_ptr);
+static int srp_compl_thread(void *target_ptr);
static void srp_send_completion(struct ib_cq *cq, void *target_ptr);
static int srp_cm_handler(struct ib_cm_id *cm_id, struct ib_cm_event *event);
@@ -229,7 +239,9 @@ static int srp_create_target_ib(struct srp_target_port
*target)
return -ENOMEM;
target->recv_cq = ib_create_cq(target->srp_host->srp_dev->dev,
- srp_recv_completion, NULL, target,
SRP_RQ_SIZE, 0);
+ thread ? srp_notify_recv_thread
+ : srp_recv_completion,
+ NULL, target, SRP_RQ_SIZE, 0);
if (IS_ERR(target->recv_cq)) {
ret = PTR_ERR(target->recv_cq);
goto err;
@@ -242,7 +254,18 @@ static int srp_create_target_ib(struct srp_target_port
*target)
goto err_recv_cq;
}
- ib_req_notify_cq(target->recv_cq, IB_CQ_NEXT_COMP);
+ if (thread) {
+ init_waitqueue_head(&target->wait_queue);
+ target->thread = kthread_run(srp_compl_thread, target,
+ "ib_srp_compl");
+ if (IS_ERR(target->thread)) {
+ ret = PTR_ERR(target->thread);
+ goto err_send_cq;
+ }
+ } else {
+ target->thread = NULL;
+ ib_req_notify_cq(target->recv_cq, IB_CQ_NEXT_COMP);
+ }
init_attr->event_handler = srp_qp_event;
init_attr->cap.max_send_wr = SRP_SQ_SIZE;
@@ -257,7 +280,7 @@ static int srp_create_target_ib(struct srp_target_port
*target)
target->qp = ib_create_qp(target->srp_host->srp_dev->pd, init_attr);
if (IS_ERR(target->qp)) {
ret = PTR_ERR(target->qp);
- goto err_send_cq;
+ goto err_thread;
}
ret = srp_init_qp(target, target->qp);
@@ -270,6 +293,10 @@ static int srp_create_target_ib(struct srp_target_port
*target)
err_qp:
ib_destroy_qp(target->qp);
+err_thread:
+ if (target->thread)
+ kthread_stop(target->thread);
+
err_send_cq:
ib_destroy_cq(target->send_cq);
@@ -286,6 +313,8 @@ static void srp_free_target_ib(struct srp_target_port
*target)
int i;
ib_destroy_qp(target->qp);
+ if (target->thread)
+ kthread_stop(target->thread);
ib_destroy_cq(target->send_cq);
ib_destroy_cq(target->recv_cq);
@@ -917,23 +946,45 @@ static void srp_handle_recv(struct srp_target_port
*target, struct ib_wc *wc)
DMA_FROM_DEVICE);
}
+static void srp_notify_recv_thread(struct ib_cq *cq, void *target_ptr)
+{
+ struct srp_target_port *target = target_ptr;
+
+ wake_up_interruptible(&target->wait_queue);
+}
+
static void srp_recv_completion(struct ib_cq *cq, void *target_ptr)
{
struct srp_target_port *target = target_ptr;
struct ib_wc wc;
- ib_req_notify_cq(cq, IB_CQ_NEXT_COMP);
- while (ib_poll_cq(cq, 1, &wc) > 0) {
- if (wc.status) {
- shost_printk(KERN_ERR, target->scsi_host,
- PFX "failed receive status %d\n",
- wc.status);
- target->qp_in_error = 1;
- break;
+ do {
+ while (ib_poll_cq(cq, 1, &wc) > 0) {
+ if (wc.status) {
+ shost_printk(KERN_ERR, target->scsi_host,
+ PFX "failed receive status %d\n",
+ wc.status);
+ target->qp_in_error = 1;
+ return;
+ }
+
+ srp_handle_recv(target, &wc);
}
+ } while (ib_req_notify_cq(cq, IB_CQ_NEXT_COMP
+ | IB_CQ_REPORT_MISSED_EVENTS) > 0);
+}
+
+static int srp_compl_thread(void *target_ptr)
+{
+ struct srp_target_port *target = target_ptr;
- srp_handle_recv(target, &wc);
+ while (!kthread_should_stop()) {
+ wait_event_interruptible(target->wait_queue,
+ (srp_recv_completion(target->recv_cq, target),
+ kthread_should_stop()));
}
+
+ return 0;
}
static void srp_send_completion(struct ib_cq *cq, void *target_ptr)
diff --git a/drivers/infiniband/ulp/srp/ib_srp.h
b/drivers/infiniband/ulp/srp/ib_srp.h
index 5a80eac..5ceb4a4 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.h
+++ b/drivers/infiniband/ulp/srp/ib_srp.h
@@ -129,6 +129,8 @@ struct srp_target_port {
struct ib_sa_query *path_query;
int path_query_id;
+ wait_queue_head_t wait_queue;
+ struct task_struct *thread;
struct ib_cm_id *cm_id;
struct ib_cq *recv_cq;
struct ib_cq *send_cq;
--
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