linux-kernel - Re: [PATCH v5 for-next 3/3] IB/core: Obtain subnet

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Date:   Thu, 24 Jun 2021 14:54:58 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Anand Khoje <anand.a.khoje@...cle.com>
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        dledford@...hat.com, haakon.bugge@...cle.com, leon@...nel.org
Subject: Re: [PATCH v5 for-next 3/3] IB/core: Obtain subnet_prefix from cache
 in IB devices

On Wed, Jun 23, 2021 at 06:33:32PM +0530, Anand Khoje wrote:
> On 6/22/2021 5:19 AM, Jason Gunthorpe wrote:
> > On Wed, Jun 16, 2021 at 09:15:09PM +0530, Anand Khoje wrote:
> > > @@ -1523,13 +1524,21 @@ static int config_non_roce_gid_cache(struct ib_device *device,
> > >   	device->port_data[port].cache.lmc = tprops->lmc;
> > >   	device->port_data[port].cache.port_state = tprops->state;
> > > -	device->port_data[port].cache.subnet_prefix = tprops->subnet_prefix;
> > > +	ret = rdma_query_gid(device, port, 0, &gid);
> > > +	if (ret) {
> > 
> > This is quite a bit different than just calling ops.query_gid() - why
> > are you changing it? I'm not sure all the additional tests will pass,
> > the 0 gid entry is not required to be valid..
> > 
> Hi Jason,
> 
> We have opted for rdma_query_gid(), as during ib_cache_update() the code
> calls ops.query_gid() earlier in config_non_roce_gid_cache(), thereby
> updating the value of GID in cache. We utilize this updated value, instead
> of calling ops->query_gid() again.

Uhhhh, so just store the subnet prefix at that point then?

diff --git a/drivers/infiniband/core/cache.c b/drivers/infiniband/core/cache.c
index c9e9fc81447e89..5c554ebd000e89 100644
--- a/drivers/infiniband/core/cache.c
+++ b/drivers/infiniband/core/cache.c
@@ -1428,8 +1428,8 @@ int rdma_read_gid_l2_fields(const struct ib_gid_attr *attr,
 }
 EXPORT_SYMBOL(rdma_read_gid_l2_fields);
 
-static int config_non_roce_gid_cache(struct ib_device *device,
-				     u32 port, int gid_tbl_len)
+static int config_non_roce_gid_cache(struct ib_device *device, u32 port,
+				     struct ib_port_attr *tprops)
 {
 	struct ib_gid_attr gid_attr = {};
 	struct ib_gid_table *table;
@@ -1441,7 +1441,7 @@ static int config_non_roce_gid_cache(struct ib_device *device,
 	table = rdma_gid_table(device, port);
 
 	mutex_lock(&table->lock);
-	for (i = 0; i < gid_tbl_len; ++i) {
+	for (i = 0; i < tprops->gid_tbl_len; ++i) {
 		if (!device->ops.query_gid)
 			continue;
 		ret = device->ops.query_gid(device, port, i, &gid_attr.gid);
@@ -1452,6 +1452,8 @@ static int config_non_roce_gid_cache(struct ib_device *device,
 			goto err;
 		}
 		gid_attr.index = i;
+		tprops->subnet_prefix =
+			be64_to_cpu(gid_attr.global.subnet_prefix);
 		add_modify_gid(table, &gid_attr);
 	}
 err:
@@ -1484,7 +1486,7 @@ ib_cache_update(struct ib_device *device, u32 port, bool update_gids,
 
 	if (!rdma_protocol_roce(device, port) && update_gids) {
 		ret = config_non_roce_gid_cache(device, port,
-						tprops->gid_tbl_len);
+						tprops);
 		if (ret)
 			goto err;
 	}

> > And I would much prefer things be re-organized so the cache can be
> > valid sooner to adding this variable. What is the earlier call that is
> > motivating this?
> 
> During device load and when cache is yet to be updated, ib_query_port()
> should have a mechanism to identify if the cache entry is valid or invalid
> (uninitialized), we have added this variable just to ensure the validity of
> cache.

Unless there is an actual user of ib_query_port() before
config_non_roce_gid_cache() that I can't see, don't bother, returning
0 is fine.

Jason