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Date: Wed, 19 Jan 2022 14:08:48 +0000 From: Praveen Kannoju <praveen.kannoju@...cle.com> To: Jason Gunthorpe <jgg@...pe.ca> 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 -----Original Message----- From: Jason Gunthorpe [mailto:jgg@...pe.ca] Sent: 19 January 2022 06:47 PM 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; netdev@...r.kernel.org; linux-rdma@...r.kernel.org; rds-devel@....oracle.com; 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 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(). 3. In case the function "rds_ib_free_mr", misses to spawn the flush function, the same will be requested by the allocation path "rds_ib_alloc_frmr" which in-turn calls "rds_ib_try_reuse_ibmr", which finally calls the flush function "rds_ib_flush_mr_pool" to obtain mr, during mr allocation requests. 4. If you still insist, we can modify the patch to use smp_load_acquire() and smp_store_release(). Regards, Praveen.
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