linux-kernel - Re: [PATCH rdma-next v1 6/7] RDMA/mlx5: Delay the deregistration of a non-cache mkey

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Date:   Mon, 3 Jan 2022 14:17:31 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Aharon Landau <aharonl@...dia.com>,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH rdma-next v1 6/7] RDMA/mlx5: Delay the deregistration of
 a non-cache mkey

On Sun, Jan 02, 2022 at 11:03:10AM +0800, Hillf Danton wrote:
> On Thu, 30 Dec 2021 13:23:23 +0200
> > From: Aharon Landau <aharonl@...dia.com>
> > 
> > When restarting an application with many non-cached mkeys, all the mkeys
> > will be destroyed and then recreated.
> > 
> > This process takes a long time (about 20 seconds for deregistration and
> > 28 seconds for registration of 100,000 MRs).
> > 
> > To shorten the restart runtime, insert the mkeys temporarily into the
> > cache and schedule a delayed work to destroy them later. If there is no
> > fitting entry to these mkeys, create a temporary entry that fits them.
> > 
> > If 30 seconds have passed and no user reclaimed the temporarily cached
> > mkeys, the scheduled work will destroy the mkeys and the temporary
> > entries.
> > 
> > When restarting an application, the mkeys will still be in the cache
> > when trying to reg them again, therefore, the registration will be
> > faster (4 seconds for deregistration and 5 seconds or registration of
> > 100,000 MRs).
> > 
> > Signed-off-by: Aharon Landau <aharonl@...dia.com>
> > Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> > ---
> >  drivers/infiniband/hw/mlx5/mlx5_ib.h |   3 +
> >  drivers/infiniband/hw/mlx5/mr.c      | 131 ++++++++++++++++++++++++++-
> >  2 files changed, 132 insertions(+), 2 deletions(-)

<...>

> > +	if (!ent->is_tmp)
> > +		mr->mmkey.cache_ent = ent;
> > +	else {
> > +		ent->total_mrs--;
> > +		cancel_delayed_work(&ent->dev->cache.remove_ent_dwork);
> > +		queue_delayed_work(ent->dev->cache.wq,
> > +				   &ent->dev->cache.remove_ent_dwork,
> > +				   msecs_to_jiffies(30 * 1000));
> > +	}
> 
> Nit: collapse cancel and queue into mod_delayed_work().
> 
> >  }

<...>

> > +	INIT_WORK(&ent->work, cache_work_func);
> > +	INIT_DELAYED_WORK(&ent->dwork, delayed_cache_work_func);
> 
> More important IMHO is to cut work in a seperate patch given that dwork can
> be queued with zero delay and both work callbacks are simple wrappers of
> __cache_work_func(). 

Thanks, I'll collect more feedback and resubmit.

> 
> Hillf