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IB/srp: allow lockless work posting
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Only one CPU at a time will own an RX IU, so using the address of the IU
as the work request cookie allows us to avoid taking a lock. We can
similarly prepare the TX path for lockless posting by moving the free TX
IUs to a list. This also removes the requirement that the queue sizes be
a power of 2.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
[ broken out, small cleanups, and modified to avoid needing an extra field
  in the IU by David Dillow]
Signed-off-by: David Dillow <dillowda@ornl.gov>
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Bart Van Assche authored and David Dillow committed Jan 5, 2011
1 parent 9709f0e commit dcb4cb8
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Showing 2 changed files with 28 additions and 44 deletions.
65 changes: 26 additions & 39 deletions drivers/infiniband/ulp/srp/ib_srp.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -568,7 +568,7 @@ static int srp_reconnect_target(struct srp_target_port *target)
struct ib_qp_attr qp_attr;
struct srp_request *req, *tmp;
struct ib_wc wc;
int ret;
int i, ret;

if (!srp_change_state(target, SRP_TARGET_LIVE, SRP_TARGET_CONNECTING))
return -EAGAIN;
Expand Down Expand Up @@ -601,9 +601,9 @@ static int srp_reconnect_target(struct srp_target_port *target)
srp_reset_req(target, req);
spin_unlock_irq(target->scsi_host->host_lock);

target->rx_head = 0;
target->tx_head = 0;
target->tx_tail = 0;
list_del_init(&target->free_tx);
for (i = 0; i < SRP_SQ_SIZE; ++i)
list_move(&target->tx_ring[i]->list, &target->free_tx);

target->qp_in_error = 0;
ret = srp_connect_target(target);
Expand Down Expand Up @@ -817,7 +817,7 @@ static int srp_map_data(struct scsi_cmnd *scmnd, struct srp_target_port *target,

/*
* Must be called with target->scsi_host->host_lock held to protect
* req_lim and tx_head. Lock cannot be dropped between call here and
* req_lim and free_tx. Lock cannot be dropped between call here and
* call to __srp_post_send().
*
* Note:
Expand All @@ -837,7 +837,7 @@ static struct srp_iu *__srp_get_tx_iu(struct srp_target_port *target,

srp_send_completion(target->send_cq, target);

if (target->tx_head - target->tx_tail >= SRP_SQ_SIZE)
if (list_empty(&target->free_tx))
return NULL;

/* Initiator responses to target requests do not consume credits */
Expand All @@ -846,14 +846,14 @@ static struct srp_iu *__srp_get_tx_iu(struct srp_target_port *target,
return NULL;
}

iu = target->tx_ring[target->tx_head & SRP_SQ_MASK];
iu = list_first_entry(&target->free_tx, struct srp_iu, list);
iu->type = iu_type;
return iu;
}

/*
* Must be called with target->scsi_host->host_lock held to protect
* req_lim and tx_head.
* req_lim and free_tx.
*/
static int __srp_post_send(struct srp_target_port *target,
struct srp_iu *iu, int len)
Expand All @@ -867,7 +867,7 @@ static int __srp_post_send(struct srp_target_port *target,
list.lkey = target->srp_host->srp_dev->mr->lkey;

wr.next = NULL;
wr.wr_id = target->tx_head & SRP_SQ_MASK;
wr.wr_id = (uintptr_t) iu;
wr.sg_list = &list;
wr.num_sge = 1;
wr.opcode = IB_WR_SEND;
Expand All @@ -876,44 +876,29 @@ static int __srp_post_send(struct srp_target_port *target,
ret = ib_post_send(target->qp, &wr, &bad_wr);

if (!ret) {
++target->tx_head;
list_del(&iu->list);
if (iu->type != SRP_IU_RSP)
--target->req_lim;
}

return ret;
}

static int srp_post_recv(struct srp_target_port *target)
static int srp_post_recv(struct srp_target_port *target, struct srp_iu *iu)
{
unsigned long flags;
struct srp_iu *iu;
struct ib_sge list;
struct ib_recv_wr wr, *bad_wr;
unsigned int next;
int ret;

spin_lock_irqsave(target->scsi_host->host_lock, flags);

next = target->rx_head & SRP_RQ_MASK;
wr.wr_id = next;
iu = target->rx_ring[next];
struct ib_sge list;

list.addr = iu->dma;
list.length = iu->size;
list.lkey = target->srp_host->srp_dev->mr->lkey;

wr.next = NULL;
wr.wr_id = (uintptr_t) iu;
wr.sg_list = &list;
wr.num_sge = 1;

ret = ib_post_recv(target->qp, &wr, &bad_wr);
if (!ret)
++target->rx_head;

spin_unlock_irqrestore(target->scsi_host->host_lock, flags);

return ret;
return ib_post_recv(target->qp, &wr, &bad_wr);
}

static void srp_process_rsp(struct srp_target_port *target, struct srp_rsp *rsp)
Expand Down Expand Up @@ -1030,14 +1015,11 @@ static void srp_process_aer_req(struct srp_target_port *target,

static void srp_handle_recv(struct srp_target_port *target, struct ib_wc *wc)
{
struct ib_device *dev;
struct srp_iu *iu;
struct ib_device *dev = target->srp_host->srp_dev->dev;
struct srp_iu *iu = (struct srp_iu *) wc->wr_id;
int res;
u8 opcode;

iu = target->rx_ring[wc->wr_id];

dev = target->srp_host->srp_dev->dev;
ib_dma_sync_single_for_cpu(dev, iu->dma, target->max_ti_iu_len,
DMA_FROM_DEVICE);

Expand Down Expand Up @@ -1078,7 +1060,7 @@ static void srp_handle_recv(struct srp_target_port *target, struct ib_wc *wc)
ib_dma_sync_single_for_device(dev, iu->dma, target->max_ti_iu_len,
DMA_FROM_DEVICE);

res = srp_post_recv(target);
res = srp_post_recv(target, iu);
if (res != 0)
shost_printk(KERN_ERR, target->scsi_host,
PFX "Recv failed with error code %d\n", res);
Expand Down Expand Up @@ -1107,6 +1089,7 @@ static void srp_send_completion(struct ib_cq *cq, void *target_ptr)
{
struct srp_target_port *target = target_ptr;
struct ib_wc wc;
struct srp_iu *iu;

while (ib_poll_cq(cq, 1, &wc) > 0) {
if (wc.status) {
Expand All @@ -1117,7 +1100,8 @@ static void srp_send_completion(struct ib_cq *cq, void *target_ptr)
break;
}

++target->tx_tail;
iu = (struct srp_iu *) wc.wr_id;
list_add(&iu->list, &target->free_tx);
}
}

Expand Down Expand Up @@ -1212,6 +1196,8 @@ static int srp_alloc_iu_bufs(struct srp_target_port *target)
GFP_KERNEL, DMA_TO_DEVICE);
if (!target->tx_ring[i])
goto err;

list_add(&target->tx_ring[i]->list, &target->free_tx);
}

return 0;
Expand Down Expand Up @@ -1373,7 +1359,8 @@ static int srp_cm_handler(struct ib_cm_id *cm_id, struct ib_cm_event *event)
break;

for (i = 0; i < SRP_RQ_SIZE; i++) {
target->status = srp_post_recv(target);
struct srp_iu *iu = target->rx_ring[i];
target->status = srp_post_recv(target, iu);
if (target->status)
break;
}
Expand Down Expand Up @@ -1965,6 +1952,7 @@ static ssize_t srp_create_target(struct device *dev,
target->scsi_host = target_host;
target->srp_host = host;

INIT_LIST_HEAD(&target->free_tx);
INIT_LIST_HEAD(&target->free_reqs);
INIT_LIST_HEAD(&target->req_queue);
for (i = 0; i < SRP_CMD_SQ_SIZE; ++i) {
Expand Down Expand Up @@ -2235,8 +2223,7 @@ static int __init srp_init_module(void)
{
int ret;

BUILD_BUG_ON_NOT_POWER_OF_2(SRP_SQ_SIZE);
BUILD_BUG_ON_NOT_POWER_OF_2(SRP_RQ_SIZE);
BUILD_BUG_ON(FIELD_SIZEOF(struct ib_wc, wr_id) < sizeof(void *));

if (srp_sg_tablesize > 255) {
printk(KERN_WARNING PFX "Clamping srp_sg_tablesize to 255\n");
Expand Down
7 changes: 2 additions & 5 deletions drivers/infiniband/ulp/srp/ib_srp.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -59,10 +59,8 @@ enum {

SRP_RQ_SHIFT = 6,
SRP_RQ_SIZE = 1 << SRP_RQ_SHIFT,
SRP_RQ_MASK = SRP_RQ_SIZE - 1,

SRP_SQ_SIZE = SRP_RQ_SIZE,
SRP_SQ_MASK = SRP_SQ_SIZE - 1,
SRP_RSP_SQ_SIZE = 1,
SRP_REQ_SQ_SIZE = SRP_SQ_SIZE - SRP_RSP_SQ_SIZE,
SRP_TSK_MGMT_SQ_SIZE = 1,
Expand Down Expand Up @@ -144,11 +142,9 @@ struct srp_target_port {

int zero_req_lim;

unsigned rx_head;
struct srp_iu *rx_ring[SRP_RQ_SIZE];

unsigned tx_head;
unsigned tx_tail;
struct list_head free_tx;
struct srp_iu *tx_ring[SRP_SQ_SIZE];

struct list_head free_reqs;
Expand All @@ -168,6 +164,7 @@ struct srp_target_port {
};

struct srp_iu {
struct list_head list;
u64 dma;
void *buf;
size_t size;
Expand Down

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