From: okaya@codeaurora.org
To: Casey Leedom <leedom@chelsio.com>
Cc: netdev@vger.kernel.org, timur@codeaurora.org,
sulrich@codeaurora.org, linux-arm-msm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Ganesh GR <ganeshgr@chelsio.com>,
linux-kernel@vger.kernel.org, Michael Werner <werner@chelsio.com>,
SWise OGC <swise@opengridcomputing.com>
Subject: Re: [PATCH v4 12/17] net: cxgb4/cxgb4vf: Eliminate duplicate barriers on weakly-ordered archs
Date: Wed, 21 Mar 2018 20:00:58 -0400 [thread overview]
Message-ID: <11820921c76403bca743c382287aee05@codeaurora.org> (raw)
In-Reply-To: <BY2PR1201MB0983417DC5ECAB85834A84DBC8AA0@BY2PR1201MB0983.namprd12.prod.outlook.com>
On 2018-03-21 19:03, Casey Leedom wrote:
> [[ Appologies for the DUPLICATE email. I forgot to tell my Mail Agent
> to
> use Plain Text. -- Casey ]]
>
> I feel very uncomfortable with these proposed changes. Our team is
> right
> in the middle of trying to tease our way through the various platform
> implementations of writel(), writel_relaxed(), __raw_writel(), etc. in
> order
> to support x86, PowerPC, ARM, etc. with a single code base. This is
> complicated by the somewhat ... "fuzzily defined" semantics and varying
> platform implementations of all of these APIs. (And note that I'm just
> picking writel() as an example.)
>
> Additionally, many of the changes aren't even in fast paths and are
> thus
> unneeded for performance.
>
> Please don't make these changes. We're trying to get this all sussed
> out.
>
I was also given the feedback to look at performance critical path only.
I am in the process of revisiting the patches.
If you can point me to the ones that are important, I can try to limit
the changes to those only.
If your team wants to do it, I can drop this patch as well.
I think the semantics of write API is clear. What was actually
implemented is another story.
I can share a few of my findings.
A portable driver needs to do this.
descriptor update in mem
wmb ()
writel_relaxed ()
mmiowb ()
Using __raw_write() is wrong as it can get reordered.
Using wmb()+writel() is also wrong for performance reasons.
If something is unclear, please ask.
>
next prev parent reply other threads:[~2018-03-22 0:00 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-20 2:42 [PATCH v4 00/17] netdev: Eliminate duplicate barriers on weakly-ordered archs Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 01/17] i40e/i40evf: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 02/17] ixgbe: eliminate " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 03/17] igbvf: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 04/17] igb: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 05/17] ixgbevf: keep writel() closer to wmb() Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 06/17] ixgbevf: eliminate duplicate barriers on weakly-ordered archs Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 07/17] fm10k: Eliminate " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 08/17] drivers: net: cxgb: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 09/17] net: qla3xxx: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 10/17] qlcnic: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 11/17] bnx2x: " Sinan Kaya
2018-03-22 10:10 ` Kalluru, Sudarsana
2018-03-20 2:42 ` [PATCH v4 12/17] net: cxgb4/cxgb4vf: " Sinan Kaya
2018-03-21 23:03 ` Casey Leedom
2018-03-22 0:00 ` okaya [this message]
2018-03-20 2:42 ` [PATCH v4 13/17] net: cxgb3: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 14/17] net: qlge: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 15/17] bnxt_en: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 16/17] qed/qede: " Sinan Kaya
2018-03-20 2:42 ` [PATCH v4 17/17] net: ena: " Sinan Kaya
2018-03-25 12:06 ` Belgazal, Netanel
2018-03-25 13:33 ` okaya
2018-03-21 15:56 ` [PATCH v4 00/17] netdev: " David Miller
2018-03-21 19:06 ` Sinan Kaya
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