Commit 4da68744 authored by D. Wythe's avatar D. Wythe Committed by David S. Miller

net/smc: reduce unnecessary blocking in smcr_lgr_reg_rmbs()

Unlike smc_buf_create() and smcr_buf_unuse(), smcr_lgr_reg_rmbs() is
exclusive when assigned rmb_desc was not registered, although it can be
executed in parallel when assigned rmb_desc was registered already
and only performs read semtamics on it. Hence, we can not simply replace
it with read semaphore.

The idea here is that if the assigned rmb_desc was registered already,
use read semaphore to protect the critical section, once the assigned
rmb_desc was not registered, keep using keep write semaphore still
to keep its exclusivity.

Thanks to the reusable features of rmb_desc, which allows us to execute
in parallel in most cases.
Signed-off-by: default avatarD. Wythe <alibuda@linux.alibaba.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f6421014
......@@ -519,11 +519,26 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link,
struct smc_buf_desc *rmb_desc)
{
struct smc_link_group *lgr = link->lgr;
bool do_slow = false;
int i, rc = 0;
rc = smc_llc_flow_initiate(lgr, SMC_LLC_FLOW_RKEY);
if (rc)
return rc;
down_read(&lgr->llc_conf_mutex);
for (i = 0; i < SMC_LINKS_PER_LGR_MAX; i++) {
if (!smc_link_active(&lgr->lnk[i]))
continue;
if (!rmb_desc->is_reg_mr[link->link_idx]) {
up_read(&lgr->llc_conf_mutex);
goto slow_path;
}
}
/* mr register already */
goto fast_path;
slow_path:
do_slow = true;
/* protect against parallel smc_llc_cli_rkey_exchange() and
* parallel smcr_link_reg_buf()
*/
......@@ -535,7 +550,7 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link,
if (rc)
goto out;
}
fast_path:
/* exchange confirm_rkey msg with peer */
rc = smc_llc_do_confirm_rkey(link, rmb_desc);
if (rc) {
......@@ -544,7 +559,7 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link,
}
rmb_desc->is_conf_rkey = true;
out:
up_write(&lgr->llc_conf_mutex);
do_slow ? up_write(&lgr->llc_conf_mutex) : up_read(&lgr->llc_conf_mutex);
smc_llc_flow_stop(lgr, &lgr->llc_flow_lcl);
return rc;
}
......
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