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

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

net/smc/af_smc.c

+17 −2
Original line number Diff line number Diff line
@@ -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;

}