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Date: Wed, 16 Jun 2021 11:41:29 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Anand Khoje <anand.a.khoje@...cle.com>
Cc: linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
dledford@...hat.com, jgg@...pe.ca, haakon.bugge@...cle.com
Subject: Re: [PATCH v4 for-next 3/3] IB/core: Obtain subnet_prefix from cache
in IB devices
On Wed, Jun 16, 2021 at 01:12:51PM +0530, Anand Khoje wrote:
> On 6/16/2021 12:57 PM, Leon Romanovsky wrote:
> > On Wed, Jun 16, 2021 at 12:22:13PM +0530, Anand Khoje wrote:
> > > ib_query_port() calls device->ops.query_port() to get the port
> > > attributes. The method of querying is device driver specific.
> > > The same function calls device->ops.query_gid() to get the GID and
> > > extract the subnet_prefix (gid_prefix).
> > >
> > > The GID and subnet_prefix are stored in a cache. But they do not get
> > > read from the cache if the device is an Infiniband device. The
> > > following change takes advantage of the cached subnet_prefix.
> > > Testing with RDBMS has shown a significant improvement in performance
> > > with this change.
> > >
> > > The function ib_cache_is_initialised() is introduced because
> > > ib_query_port() gets called early in the stage when the cache is not
> > > built while reading port immutable property.
> > >
> > > In that case, the default GID still gets read from HCA for IB link-
> > > layer devices.
> > >
> > > In the situation of an event causing cache update, the subnet_prefix
> > > will get retrieved from newly updated GID cache in ib_cache_update(),
> > > so that we do not end up reading a stale value from cache via
> > > ib_query_port().
> > >
> > > Fixes: fad61ad ("IB/core: Add subnet prefix to port info")
> > > Suggested-by: Leon Romanovsky <leonro@...dia.com>
> > > Suggested-by: Aru Kolappan <aru.kolappan@...cle.com>
> > > Signed-off-by: Anand Khoje <anand.a.khoje@...cle.com>
> > > Signed-off-by: Haakon Bugge <haakon.bugge@...cle.com>
> > > ---
> > >
> > > v1 -> v2:
> > > - Split the v1 patch in 3 patches as per Leon's suggestion.
> > >
> > > v2 -> v3:
> > > - Added changes as per Mark Zhang's suggestion of clearing
> > > flags in git_table_cleanup_one().
> > > v3 -> v4:
> > > - Removed the enum ib_port_data_flags and 8 byte flags from
> > > struct ib_port_data, and the set_bit()/clear_bit() API
> > > used to update this flag as that was not necessary.
> > > Done to keep the code simple.
> > > - Added code to read subnet_prefix from updated GID cache in the
> > > event of cache update. Prior to this change, ib_cache_update
> > > was reading the value for subnet_prefix via ib_query_port(),
> > > due to this patch, we ended up reading a stale cached value of
> > > subnet_prefix.
> > >
> > > ---
> > > drivers/infiniband/core/cache.c | 18 +++++++++++++++---
> > > drivers/infiniband/core/device.c | 9 +++++++++
> > > include/rdma/ib_cache.h | 5 +++++
> > > include/rdma/ib_verbs.h | 1 +
> > > 4 files changed, 30 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/infiniband/core/cache.c b/drivers/infiniband/core/cache.c
> > > index 2325171..cd99c46 100644
> > > --- a/drivers/infiniband/core/cache.c
> > > +++ b/drivers/infiniband/core/cache.c
> > > @@ -917,9 +917,11 @@ static void gid_table_cleanup_one(struct ib_device *ib_dev)
> > > {
> > > u32 p;
> > > - rdma_for_each_port (ib_dev, p)
> > > + rdma_for_each_port (ib_dev, p) {
> > > + ib_dev->port_data[p].cache_is_initialized = 0;
> >
> > I think that this line is not needed, we are removing device anyway and
> > and query_port is not allowed at this stage.
> >
> We have kept this for code completeness purposes. Just as we did with
> set_bit() and clear_bit() APIs.
You are not using *_bit() API now, so let's not clear here.
It is not completeness, but misleading. It gives false assumption
that cache_is_initialized is used later in the code.
>
> > > cleanup_gid_table_port(ib_dev, p,
> > > ib_dev->port_data[p].cache.gid);
> > > + }
> > > }
> > > static int gid_table_setup_one(struct ib_device *ib_dev)
> > > @@ -1466,6 +1468,7 @@ static int config_non_roce_gid_cache(struct ib_device *device,
> > > struct ib_port_attr *tprops = NULL;
> > > struct ib_pkey_cache *pkey_cache = NULL;
> > > struct ib_pkey_cache *old_pkey_cache = NULL;
> > > + union ib_gid gid;
> > > int i;
> > > int ret;
> > > @@ -1523,13 +1526,21 @@ 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) {
> > > + write_unlock_irq(&device->cache.lock);
> > > + goto err;
> > > + }
> > > +
> > > + device->port_data[port].cache.subnet_prefix =
> > > + be64_to_cpu(gid.global.subnet_prefix);
> > > +
> > > write_unlock_irq(&device->cache_lock);
> > > if (enforce_security)
> > > ib_security_cache_change(device,
> > > port,
> > > - tprops->subnet_prefix);
> > > + be64_to_cpu(gid.global.subnet_prefix));
> > > kfree(old_pkey_cache);
> > > kfree(tprops);
> > > @@ -1629,6 +1640,7 @@ int ib_cache_setup_one(struct ib_device *device)
> > > err = ib_cache_update(device, p, true, true, true);
> > > if (err)
> > > return err;
> > > + device->port_data[p].cache_is_initialized = 1;
> > > }
> > > return 0;
> > > diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
> > > index 7a617e4..57b9039 100644
> > > --- a/drivers/infiniband/core/device.c
> > > +++ b/drivers/infiniband/core/device.c
> > > @@ -2057,6 +2057,15 @@ static int __ib_query_port(struct ib_device *device,
> > > IB_LINK_LAYER_INFINIBAND)
> > > return 0;
> > > + if (!ib_cache_is_initialised(device, port_num))
> > > + goto query_gid_from_device;
> >
> > IMHO, we don't need this new function and can access ib_port_data
> > directly. In device.c, we have plenty of places that does it.
> >
> > Not critical.
> >
> Added this function to have a way to check validity of cache, such that it
> could be used in future for the same check in areas to which ib_port_data is
> opaque.
It is ok, just call directly if (!device->port_data[port_num].cache_is_initialized).
Thanks
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