From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH v7 0/7] netdev: Eliminate duplicate barriers on weakly-ordered archs Date: Mon, 26 Mar 2018 12:48:46 -0400 (EDT) Message-ID: <20180326.124846.2182144342929084561.davem@davemloft.net> References: <1521988761-30344-1-git-send-email-okaya@codeaurora.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1521988761-30344-1-git-send-email-okaya@codeaurora.org> Sender: netdev-owner@vger.kernel.org To: okaya@codeaurora.org Cc: netdev@vger.kernel.org, timur@codeaurora.org, sulrich@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org List-Id: linux-arm-msm@vger.kernel.org From: Sinan Kaya Date: Sun, 25 Mar 2018 10:39:14 -0400 > Code includes wmb() followed by writel() in multiple places. writel() > already has a barrier on some architectures like arm64. > > This ends up CPU observing two barriers back to back before executing the > register write. > > Since code already has an explicit barrier call, changing writel() to > writel_relaxed(). > > I did a regex search for wmb() followed by writel() in each drivers > directory. > I scrubbed the ones I care about in this series. > > I considered "ease of change", "popular usage" and "performance critical > path" as the determining criteria for my filtering. > > We used relaxed API heavily on ARM for a long time but > it did not exist on other architectures. For this reason, relaxed > architectures have been paying double penalty in order to use the common > drivers. > > Now that relaxed API is present on all architectures, we can go and scrub > all drivers to see what needs to change and what can remain. > > We start with mostly used ones and hope to increase the coverage over time. > It will take a while to cover all drivers. > > Feel free to apply patches individually. > > Changes since v6: > - bring back amazon ena and add mmiowb, remove > ena_com_write_sq_doorbell_rel(). > - remove extra mmiowb in bnx2x > - correct spelling mistake in bnx2x: Replace doorbell barrier() with wmb() Series applied, thank you. From mboxrd@z Thu Jan 1 00:00:00 1970 From: davem@davemloft.net (David Miller) Date: Mon, 26 Mar 2018 12:48:46 -0400 (EDT) Subject: [PATCH v7 0/7] netdev: Eliminate duplicate barriers on weakly-ordered archs In-Reply-To: <1521988761-30344-1-git-send-email-okaya@codeaurora.org> References: <1521988761-30344-1-git-send-email-okaya@codeaurora.org> Message-ID: <20180326.124846.2182144342929084561.davem@davemloft.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Sinan Kaya Date: Sun, 25 Mar 2018 10:39:14 -0400 > Code includes wmb() followed by writel() in multiple places. writel() > already has a barrier on some architectures like arm64. > > This ends up CPU observing two barriers back to back before executing the > register write. > > Since code already has an explicit barrier call, changing writel() to > writel_relaxed(). > > I did a regex search for wmb() followed by writel() in each drivers > directory. > I scrubbed the ones I care about in this series. > > I considered "ease of change", "popular usage" and "performance critical > path" as the determining criteria for my filtering. > > We used relaxed API heavily on ARM for a long time but > it did not exist on other architectures. For this reason, relaxed > architectures have been paying double penalty in order to use the common > drivers. > > Now that relaxed API is present on all architectures, we can go and scrub > all drivers to see what needs to change and what can remain. > > We start with mostly used ones and hope to increase the coverage over time. > It will take a while to cover all drivers. > > Feel free to apply patches individually. > > Changes since v6: > - bring back amazon ena and add mmiowb, remove > ena_com_write_sq_doorbell_rel(). > - remove extra mmiowb in bnx2x > - correct spelling mistake in bnx2x: Replace doorbell barrier() with wmb() Series applied, thank you.