From: "Nikolova, Tatyana E" <tatyana.e.nikolova@intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: "dledford@redhat.com" <dledford@redhat.com>,
"leon@kernel.org" <leon@kernel.org>,
"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>
Subject: RE: [PATCH rdma-core] irdma: Restore full memory barrier for doorbell optimization
Date: Thu, 19 Aug 2021 22:01:50 +0000 [thread overview]
Message-ID: <DM6PR11MB4692DCA80480234AAD298313CBC09@DM6PR11MB4692.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20210818164931.GC5673@nvidia.com>
> -----Original Message-----
> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, August 18, 2021 11:50 AM
> To: Nikolova, Tatyana E <tatyana.e.nikolova@intel.com>
> Cc: dledford@redhat.com; leon@kernel.org; linux-rdma@vger.kernel.org
> Subject: Re: [PATCH rdma-core] irdma: Restore full memory barrier for
> doorbell optimization
>
> On Fri, Aug 13, 2021 at 05:25:49PM -0500, Tatyana Nikolova wrote:
> > >> 1. Software writing the valid bit in the WQE.
> > >> 2. Software reading shadow memory (hw_tail) value.
> >
> > > You are missing an ordered atomic on this read it looks like
> >
> > Hi Jason,
> >
> > Why do you think we need atomic ops in this case? We aren't trying to
> > protect from multiple threads but CPU re-ordering of a write and a
> > read.
>
> Which is what the atomics will do.
>
> Barriers are only appropriate when you can't add atomic markers to the
> actual data that needs ordering.
Hi Jason,
We aren't sure what you mean by atomic markers. We ran a few experiments with atomics, but none of the barriers we tried smp_mb__{before,after}_atomic(), smp_load_acquire() and smp_store_release() translates to a full memory barrier on X86.
Could you give us an example?
Thank you,
Tatyana
next prev parent reply other threads:[~2021-08-19 22:01 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-05 16:11 [PATCH rdma-core] irdma: Restore full memory barrier for doorbell optimization Tatyana Nikolova
2021-08-06 1:28 ` Jason Gunthorpe
2021-08-09 20:07 ` Nikolova, Tatyana E
2021-08-10 11:59 ` Jason Gunthorpe
2021-08-13 22:25 ` Tatyana Nikolova
2021-08-18 16:49 ` Jason Gunthorpe
2021-08-19 22:01 ` Nikolova, Tatyana E [this message]
2021-08-19 22:44 ` Jason Gunthorpe
2021-09-02 16:27 ` Nikolova, Tatyana E
2021-09-02 17:09 ` Jason Gunthorpe
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