linux-kernel - Re: [PATCH RFC] rds: ib: Reduce the contention caused by the asynchronous workers to flush the mr pool

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Message-ID: <20220119130450.GJ8034@ziepe.ca>
Date:   Wed, 19 Jan 2022 09:04:50 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Praveen Kannoju <praveen.kannoju@...cle.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        "David S . Miller" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "rds-devel@....oracle.com" <rds-devel@....oracle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rama Nichanamatlu <rama.nichanamatlu@...cle.com>,
        Rajesh Sivaramasubramaniom 
        <rajesh.sivaramasubramaniom@...cle.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 11:46:16AM +0000, Praveen Kannoju wrote:
 
> 6. Jason, the only function "rds_ib_free_mr" which accesses the
> introduced bool variable "flush_ongoing" to spawn a flush worker
> does not crucially impact the availability of MR's, because the
> flush happens from allocation path as well when necessary.  Hence
> the Load-store ordering is not essentially needed here, because of
> which we chose smp_rmb() and smp_wmb() over smp_load_acquire() and
> smp_store_release().

That seems like a confusing statement, you added barriers which do the
same things as acquire/release then say you didn't need acquire
release?

I think this is using barriers wrong.

Jason