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target: Drop iSCSI use of mutex around max_cmd_sn increment
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In a performance profile, taking a mutex in iscsit_increment_maxcmdsn()
shows up very high.  However taking a mutex around "sess->max_cmd_sn += 1"
seems pretty silly: we're not serializing against other contexts in
any useful way.

I did a quick audit and there don't appear to be any other places that
use max_cmd_sn within the mutex more than once, so this lock can't be
providing any useful serialization.

(Get correct values for logging - fix whitespace damage)

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Spencer Baugh <sbaugh@catern.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
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Roland Dreier authored and Nicholas Bellinger committed Aug 3, 2015
1 parent 24c7d6c commit 109e238
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Showing 8 changed files with 25 additions and 28 deletions.
18 changes: 9 additions & 9 deletions drivers/target/iscsi/iscsi_target.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2555,7 +2555,7 @@ static int iscsit_send_conn_drop_async_message(
cmd->stat_sn = conn->stat_sn++;
hdr->statsn = cpu_to_be32(cmd->stat_sn);
hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));
hdr->async_event = ISCSI_ASYNC_MSG_DROPPING_CONNECTION;
hdr->param1 = cpu_to_be16(cmd->logout_cid);
hdr->param2 = cpu_to_be16(conn->sess->sess_ops->DefaultTime2Wait);
Expand Down Expand Up @@ -2627,7 +2627,7 @@ iscsit_build_datain_pdu(struct iscsi_cmd *cmd, struct iscsi_conn *conn,
hdr->statsn = cpu_to_be32(0xFFFFFFFF);

hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));
hdr->datasn = cpu_to_be32(datain->data_sn);
hdr->offset = cpu_to_be32(datain->offset);

Expand Down Expand Up @@ -2838,7 +2838,7 @@ iscsit_build_logout_rsp(struct iscsi_cmd *cmd, struct iscsi_conn *conn,

iscsit_increment_maxcmdsn(cmd, conn->sess);
hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));

pr_debug("Built Logout Response ITT: 0x%08x StatSN:"
" 0x%08x Response: 0x%02x CID: %hu on CID: %hu\n",
Expand Down Expand Up @@ -2901,7 +2901,7 @@ iscsit_build_nopin_rsp(struct iscsi_cmd *cmd, struct iscsi_conn *conn,
iscsit_increment_maxcmdsn(cmd, conn->sess);

hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));

pr_debug("Built NOPIN %s Response ITT: 0x%08x, TTT: 0x%08x,"
" StatSN: 0x%08x, Length %u\n", (nopout_response) ?
Expand Down Expand Up @@ -3048,7 +3048,7 @@ static int iscsit_send_r2t(
hdr->ttt = cpu_to_be32(r2t->targ_xfer_tag);
hdr->statsn = cpu_to_be32(conn->stat_sn);
hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));
hdr->r2tsn = cpu_to_be32(r2t->r2t_sn);
hdr->data_offset = cpu_to_be32(r2t->offset);
hdr->data_length = cpu_to_be32(r2t->xfer_len);
Expand Down Expand Up @@ -3201,7 +3201,7 @@ void iscsit_build_rsp_pdu(struct iscsi_cmd *cmd, struct iscsi_conn *conn,

iscsit_increment_maxcmdsn(cmd, conn->sess);
hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));

pr_debug("Built SCSI Response, ITT: 0x%08x, StatSN: 0x%08x,"
" Response: 0x%02x, SAM Status: 0x%02x, CID: %hu\n",
Expand Down Expand Up @@ -3320,7 +3320,7 @@ iscsit_build_task_mgt_rsp(struct iscsi_cmd *cmd, struct iscsi_conn *conn,

iscsit_increment_maxcmdsn(cmd, conn->sess);
hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));

pr_debug("Built Task Management Response ITT: 0x%08x,"
" StatSN: 0x%08x, Response: 0x%02x, CID: %hu\n",
Expand Down Expand Up @@ -3575,7 +3575,7 @@ iscsit_build_text_rsp(struct iscsi_cmd *cmd, struct iscsi_conn *conn,
*/
cmd->maxcmdsn_inc = 0;
hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));

pr_debug("Built Text Response: ITT: 0x%08x, TTT: 0x%08x, StatSN: 0x%08x,"
" Length: %u, CID: %hu F: %d C: %d\n", cmd->init_task_tag,
Expand Down Expand Up @@ -3653,7 +3653,7 @@ iscsit_build_reject(struct iscsi_cmd *cmd, struct iscsi_conn *conn,
cmd->stat_sn = conn->stat_sn++;
hdr->statsn = cpu_to_be32(cmd->stat_sn);
hdr->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
hdr->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
hdr->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));

}
EXPORT_SYMBOL(iscsit_build_reject);
Expand Down
6 changes: 4 additions & 2 deletions drivers/target/iscsi/iscsi_target_configfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -656,6 +656,7 @@ static ssize_t lio_target_nacl_show_info(
struct iscsi_conn *conn;
struct se_session *se_sess;
ssize_t rb = 0;
u32 max_cmd_sn;

spin_lock_bh(&se_nacl->nacl_sess_lock);
se_sess = se_nacl->nacl_sess;
Expand Down Expand Up @@ -703,11 +704,12 @@ static ssize_t lio_target_nacl_show_info(
" Values]-----------------------\n");
rb += sprintf(page+rb, " CmdSN/WR : CmdSN/WC : ExpCmdSN"
" : MaxCmdSN : ITT : TTT\n");
max_cmd_sn = (u32) atomic_read(&sess->max_cmd_sn);
rb += sprintf(page+rb, " 0x%08x 0x%08x 0x%08x 0x%08x"
" 0x%08x 0x%08x\n",
sess->cmdsn_window,
(sess->max_cmd_sn - sess->exp_cmd_sn) + 1,
sess->exp_cmd_sn, sess->max_cmd_sn,
(max_cmd_sn - sess->exp_cmd_sn) + 1,
sess->exp_cmd_sn, max_cmd_sn,
sess->init_task_tag, sess->targ_xfer_tag);
rb += sprintf(page+rb, "----------------------[iSCSI"
" Connections]-------------------------\n");
Expand Down
7 changes: 2 additions & 5 deletions drivers/target/iscsi/iscsi_target_device.c
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@ void iscsit_determine_maxcmdsn(struct iscsi_session *sess)
* core_set_queue_depth_for_node().
*/
sess->cmdsn_window = se_nacl->queue_depth;
sess->max_cmd_sn = (sess->max_cmd_sn + se_nacl->queue_depth) - 1;
atomic_set(&sess->max_cmd_sn, (u32) atomic_read(&sess->max_cmd_sn) + se_nacl->queue_depth - 1);
}

void iscsit_increment_maxcmdsn(struct iscsi_cmd *cmd, struct iscsi_session *sess)
Expand All @@ -57,9 +57,6 @@ void iscsit_increment_maxcmdsn(struct iscsi_cmd *cmd, struct iscsi_session *sess

cmd->maxcmdsn_inc = 1;

mutex_lock(&sess->cmdsn_mutex);
sess->max_cmd_sn += 1;
pr_debug("Updated MaxCmdSN to 0x%08x\n", sess->max_cmd_sn);
mutex_unlock(&sess->cmdsn_mutex);
pr_debug("Updated MaxCmdSN to 0x%08x\n", atomic_inc_return(&sess->max_cmd_sn));
}
EXPORT_SYMBOL(iscsit_increment_maxcmdsn);
2 changes: 1 addition & 1 deletion drivers/target/iscsi/iscsi_target_login.c
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Original file line number Diff line number Diff line change
Expand Up @@ -330,7 +330,7 @@ static int iscsi_login_zero_tsih_s1(
* The FFP CmdSN window values will be allocated from the TPG's
* Initiator Node's ACL once the login has been successfully completed.
*/
sess->max_cmd_sn = be32_to_cpu(pdu->cmdsn);
atomic_set(&sess->max_cmd_sn, be32_to_cpu(pdu->cmdsn));

sess->sess_ops = kzalloc(sizeof(struct iscsi_sess_ops), GFP_KERNEL);
if (!sess->sess_ops) {
Expand Down
9 changes: 3 additions & 6 deletions drivers/target/iscsi/iscsi_target_nego.c
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Original file line number Diff line number Diff line change
Expand Up @@ -340,7 +340,6 @@ static int iscsi_target_check_first_request(
static int iscsi_target_do_tx_login_io(struct iscsi_conn *conn, struct iscsi_login *login)
{
u32 padding = 0;
struct iscsi_session *sess = conn->sess;
struct iscsi_login_rsp *login_rsp;

login_rsp = (struct iscsi_login_rsp *) login->rsp;
Expand All @@ -352,7 +351,7 @@ static int iscsi_target_do_tx_login_io(struct iscsi_conn *conn, struct iscsi_log
login_rsp->itt = login->init_task_tag;
login_rsp->statsn = cpu_to_be32(conn->stat_sn++);
login_rsp->exp_cmdsn = cpu_to_be32(conn->sess->exp_cmd_sn);
login_rsp->max_cmdsn = cpu_to_be32(conn->sess->max_cmd_sn);
login_rsp->max_cmdsn = cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));

pr_debug("Sending Login Response, Flags: 0x%02x, ITT: 0x%08x,"
" ExpCmdSN; 0x%08x, MaxCmdSN: 0x%08x, StatSN: 0x%08x, Length:"
Expand All @@ -367,10 +366,8 @@ static int iscsi_target_do_tx_login_io(struct iscsi_conn *conn, struct iscsi_log
return -1;

login->rsp_length = 0;
mutex_lock(&sess->cmdsn_mutex);
login_rsp->exp_cmdsn = cpu_to_be32(sess->exp_cmd_sn);
login_rsp->max_cmdsn = cpu_to_be32(sess->max_cmd_sn);
mutex_unlock(&sess->cmdsn_mutex);
login_rsp->exp_cmdsn = cpu_to_be32(login_rsp->exp_cmdsn);
login_rsp->max_cmdsn = cpu_to_be32(login_rsp->max_cmdsn);

return 0;
}
Expand Down
2 changes: 1 addition & 1 deletion drivers/target/iscsi/iscsi_target_tmr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,7 @@ u8 iscsit_tmr_abort_task(
pr_err("Unable to locate RefTaskTag: 0x%08x on CID:"
" %hu.\n", hdr->rtt, conn->cid);
return (iscsi_sna_gte(be32_to_cpu(hdr->refcmdsn), conn->sess->exp_cmd_sn) &&
iscsi_sna_lte(be32_to_cpu(hdr->refcmdsn), conn->sess->max_cmd_sn)) ?
iscsi_sna_lte(be32_to_cpu(hdr->refcmdsn), (u32) atomic_read(&conn->sess->max_cmd_sn))) ?
ISCSI_TMF_RSP_COMPLETE : ISCSI_TMF_RSP_NO_TASK;
}
if (ref_cmd->cmd_sn != be32_to_cpu(hdr->refcmdsn)) {
Expand Down
7 changes: 4 additions & 3 deletions drivers/target/iscsi/iscsi_target_util.c
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Original file line number Diff line number Diff line change
Expand Up @@ -233,6 +233,7 @@ struct iscsi_r2t *iscsit_get_holder_for_r2tsn(

static inline int iscsit_check_received_cmdsn(struct iscsi_session *sess, u32 cmdsn)
{
u32 max_cmdsn;
int ret;

/*
Expand All @@ -241,10 +242,10 @@ static inline int iscsit_check_received_cmdsn(struct iscsi_session *sess, u32 cm
* or order CmdSNs due to multiple connection sessions and/or
* CRC failures.
*/
if (iscsi_sna_gt(cmdsn, sess->max_cmd_sn)) {
max_cmdsn = atomic_read(&sess->max_cmd_sn);
if (iscsi_sna_gt(cmdsn, max_cmdsn)) {
pr_err("Received CmdSN: 0x%08x is greater than"
" MaxCmdSN: 0x%08x, ignoring.\n", cmdsn,
sess->max_cmd_sn);
" MaxCmdSN: 0x%08x, ignoring.\n", cmdsn, max_cmdsn);
ret = CMDSN_MAXCMDSN_OVERRUN;

} else if (cmdsn == sess->exp_cmd_sn) {
Expand Down
2 changes: 1 addition & 1 deletion include/target/iscsi/iscsi_target_core.h
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Original file line number Diff line number Diff line change
Expand Up @@ -637,7 +637,7 @@ struct iscsi_session {
/* session wide counter: expected command sequence number */
u32 exp_cmd_sn;
/* session wide counter: maximum allowed command sequence number */
u32 max_cmd_sn;
atomic_t max_cmd_sn;
struct list_head sess_ooo_cmdsn_list;

/* LIO specific session ID */
Expand Down

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