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

[Jason Gunthorpe]

On Wed, Jan 19, 2022 at 02:08:48PM +0000, Praveen Kannoju wrote:
> From: Jason Gunthorpe [mailto:jgg@xxxxxxxx] 
> Sent: 19 January 2022 06:47 PM
> To: Praveen Kannoju <praveen.kannoju@xxxxxxxxxx>
> Cc: Leon Romanovsky <leon@xxxxxxxxxx>; Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; kuba@xxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-rdma@xxxxxxxxxxxxxxx; rds-devel@xxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Rama Nichanamatlu <rama.nichanamatlu@xxxxxxxxxx>; Rajesh Sivaramasubramaniom <rajesh.sivaramasubramaniom@xxxxxxxxxx>
> 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