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Date:   Wed, 19 Jan 2022 10:49:20 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Praveen Kannoju <praveen.kannoju@oracle.com>
Cc:     Leon Romanovsky <leon@kernel.org>,
        Santosh Shilimkar <santosh.shilimkar@oracle.com>,
        "David S . Miller" <davem@davemloft.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
        "rds-devel@oss.oracle.com" <rds-devel@oss.oracle.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Rama Nichanamatlu <rama.nichanamatlu@oracle.com>,
        Rajesh Sivaramasubramaniom 
        <rajesh.sivaramasubramaniom@oracle.com>
Subject: Re: [PATCH RFC] rds: ib: Reduce the contention caused by the
 asynchronous workers to flush the mr pool
Message-ID: <20220119144920.GL8034@ziepe.ca>
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On Wed, Jan 19, 2022 at 02:08:48PM +0000, Praveen Kannoju wrote:
> From: Jason Gunthorpe [mailto:jgg@ziepe.ca] 
> Sent: 19 January 2022 06:47 PM
> To: Praveen Kannoju <praveen.kannoju@oracle.com>
> Cc: Leon Romanovsky <leon@kernel.org>; Santosh Shilimkar <santosh.shilimkar@oracle.com>; David S . Miller <davem@davemloft.net>; kuba@kernel.org; netdev@vger.kernel.org; linux-rdma@vger.kernel.org; rds-devel@oss.oracle.com; linux-kernel@vger.kernel.org; Rama Nichanamatlu <rama.nichanamatlu@oracle.com>; Rajesh Sivaramasubramaniom <rajesh.sivaramasubramaniom@oracle.com>
> Subject: Re: [PATCH RFC] rds: ib: Reduce the contention caused by the asynchronous workers to flush the mr pool
> 
> On Wed, Jan 19, 2022 at 01:12:29PM +0000, Praveen Kannoju wrote:
> 
> > Yes, we are using the barriers. I was justifying the usage of
> > smp_rmb() and smp_wmb() over smp_load_acquire() and
> > smp_store_release() in the patch.
> 
> You failed to justify it.
> 
> Jason
> 
> Apologies, if my earlier point is not clear, Jason.
> Let me reframe:
> 
> 1. The introduced bool variable "flush_ongoing", is being accessed only in the function "rds_ib_free_mr" while spawning asynchronous workers.
> 
> 2. The ordering guaranteed by smp_rmb() and smp_wmb() would be
> sufficient for such simple usage and hence we did not use
> smp_load_acquire() and smp_store_release().

Again you haven't defined why these barriers are any differnet from
acquire/release or even *what they are doing*

Jason