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net/smc: reduce unnecessary blocking in smcr_lgr_reg_rmbs()

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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: D. Wythe <alibuda@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
D. Wythe 2023-02-02 16:26:41 +08:00 • committed by David S. Miller
parent f6421014e8
commit 4da687448d
1 changed files with 17 additions and 2 deletions
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19
net/smc/af_smc.c
View file

@ -519,11 +519,26 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link,
struct smc_buf_desc *rmb_desc) struct smc_buf_desc *rmb_desc)
{ {
struct smc_link_group *lgr = link->lgr; struct smc_link_group *lgr = link->lgr;
bool do_slow = false;
int i, rc = 0; int i, rc = 0;
rc = smc_llc_flow_initiate(lgr, SMC_LLC_FLOW_RKEY); rc = smc_llc_flow_initiate(lgr, SMC_LLC_FLOW_RKEY);
if (rc) if (rc)
return 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 /* protect against parallel smc_llc_cli_rkey_exchange() and
* parallel smcr_link_reg_buf() * parallel smcr_link_reg_buf()
*/ */
@ -535,7 +550,7 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link,
if (rc) if (rc)
goto out; goto out;
} }
fast_path:
/* exchange confirm_rkey msg with peer */ /* exchange confirm_rkey msg with peer */
rc = smc_llc_do_confirm_rkey(link, rmb_desc); rc = smc_llc_do_confirm_rkey(link, rmb_desc);
if (rc) { if (rc) {
@ -544,7 +559,7 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link,
} }
rmb_desc->is_conf_rkey = true; rmb_desc->is_conf_rkey = true;
out: 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); smc_llc_flow_stop(lgr, &lgr->llc_flow_lcl);
return rc; return rc;
} }