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[209.132.180.67]) by mx.google.com with ESMTP id g61-v6si2952078plb.291.2018.03.14.18.47.57; Wed, 14 Mar 2018 18:48:12 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=jHQkjoQW; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751741AbeCOBpv (ORCPT + 99 others); Wed, 14 Mar 2018 21:45:51 -0400 Received: from mail-qt0-f193.google.com ([209.85.216.193]:45063 "EHLO mail-qt0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751390AbeCOBpt (ORCPT ); Wed, 14 Mar 2018 21:45:49 -0400 Received: by mail-qt0-f193.google.com with SMTP id v90so5611278qte.12; Wed, 14 Mar 2018 18:45:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=OEV8ZTV5THXQ/I8TDFfcKQjL8BjhsdB1qCSQLxuEdVo=; b=jHQkjoQWHyo9iGEQusetN9fxwJRN28RjIzjiK6HQXpswFG944QHzZ+ZyVzB2bQM+FL PcpQk6/mI0uxM6L3JrkCut30Sb0LSqa63SrXKIELej1uPOMtY/PdvR+4Rgf7+U7OvQYy Tv0CvByDNcDy6eHfLxm+YykcIyxGx93k1ZEJ3xO8YO+V2YS+FzNLWMTuTP2dMQ83HyGz bfwY1ErjjYlK2Ksvt50Nh3h6wgTubVtcbz5gkt3EnQlrXApdMmuQ+BgSTP5+WoGtcTvj 9WJFmq73x2A5cdW78BW15PgGoBuAK+ku06oLGPt4q2JerdUh59x+BhQy6CG5giPw4JVK ke5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=OEV8ZTV5THXQ/I8TDFfcKQjL8BjhsdB1qCSQLxuEdVo=; b=PM2D7dr7cBE6Ya8WFkLEGiwm8LmFMbh9sZ4kdi2JYh/BvMl95etqoMr+SfCIacmLW2 5qSOiBqFOBCR/6qgBWblqnbGzz/Ptyk2Gvp+dlaMhV03qs3QMNl8kiv4ZvPZANPlWcqo hrf8HXa3UhaHHndOi7oEoMUtaq6MIbbgwE+9gPlemKZ1sjW3MRVdP8qebY2IuVKwUGEr J7qEHgMJMdLBPDsn32C0XqqMT9Zj/kUWVm+jjN3mj89DB6N4lBlTUksTMlVt9I4H9OvP mGy4cWr8XKa1pB3JGHUvJUJv9VwZeZ/2lIhdPueWzcd3U+0ZVN3DPyVcSh2suXqg4z52 YSvQ== X-Gm-Message-State: AElRT7HS29is/QFQVlLvycQbQ9H7ZrFifx3hw81uu2+ySDnqPXF7eGu9 hk8C2hVgjEMhJ8o6L5kbgaIP+rqi6jS4XFX2jSk= X-Received: by 10.200.57.117 with SMTP id t50mr10910325qtb.22.1521078348196; Wed, 14 Mar 2018 18:45:48 -0700 (PDT) MIME-Version: 1.0 Received: by 10.140.89.138 with HTTP; Wed, 14 Mar 2018 18:45:47 -0700 (PDT) In-Reply-To: <1520997629-17361-7-git-send-email-okaya@codeaurora.org> References: <1520997629-17361-1-git-send-email-okaya@codeaurora.org> <1520997629-17361-7-git-send-email-okaya@codeaurora.org> From: Alexander Duyck Date: Wed, 14 Mar 2018 18:45:47 -0700 Message-ID: Subject: Re: [PATCH 7/7] ixgbevf: eliminate duplicate barriers on weakly-ordered archs To: Sinan Kaya Cc: Netdev , Timur Tabi , sulrich@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jeff Kirsher , intel-wired-lan , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 13, 2018 at 8:20 PM, Sinan Kaya wrote: > 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(). > > Signed-off-by: Sinan Kaya > --- > drivers/net/ethernet/intel/ixgbevf/ixgbevf.h | 5 ++++- > drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c | 7 +++++++ > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h b/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h > index f695242..64d0e0b 100644 > --- a/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h > +++ b/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h > @@ -244,9 +244,12 @@ static inline u16 ixgbevf_desc_unused(struct ixgbevf_ring *ring) > return ((ntc > ntu) ? 0 : ring->count) + ntc - ntu - 1; > } > > +/* Assumes caller has executed a write barrier to order memory and device > + * requests. > + */ > static inline void ixgbevf_write_tail(struct ixgbevf_ring *ring, u32 value) > { > - writel(value, ring->tail); > + writel_relaxed(value, ring->tail); > } > > #define IXGBEVF_RX_DESC(R, i) \ > diff --git a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c > index 9b3d43d..0ba7f59 100644 > --- a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c > +++ b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c > @@ -3643,6 +3643,13 @@ static void ixgbevf_tx_map(struct ixgbevf_ring *tx_ring, > > tx_ring->next_to_use = i; > > + /* Force memory writes to complete before letting h/w > + * know there are new descriptors to fetch. (Only > + * applicable for weak-ordered memory model archs, > + * such as IA-64). > + */ > + wmb(); This memory barrier is redundant. There is a wmb() that is called about 10 lines before this. > + > /* notify HW of packet */ > ixgbevf_write_tail(tx_ring, i); > > -- > 2.7.4 >