From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?iso-8859-1?Q?N=E9lio?= Laranjeiro Subject: Re: [PATCH 2/2] net/mlx5: don't map doorbell register to write combining Date: Wed, 23 Aug 2017 14:06:04 +0200 Message-ID: <20170823120604.GX12995@autoinstall.dev.6wind.com> References: <1503301622-14220-1-git-send-email-sagi@grimberg.me> <1503301622-14220-3-git-send-email-sagi@grimberg.me> <38d6d1e6-7e39-e0d6-863c-2b616f7cbe18@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Cc: Sagi Grimberg , dev@dpdk.org, Adrien Mazarguil , Shahaf Shuler To: Ferruh Yigit Return-path: Received: from mail-wm0-f46.google.com (mail-wm0-f46.google.com [74.125.82.46]) by dpdk.org (Postfix) with ESMTP id 62B447D3A for ; Wed, 23 Aug 2017 14:06:14 +0200 (CEST) Received: by mail-wm0-f46.google.com with SMTP id l19so14144333wmi.1 for ; Wed, 23 Aug 2017 05:06:14 -0700 (PDT) Content-Disposition: inline In-Reply-To: <38d6d1e6-7e39-e0d6-863c-2b616f7cbe18@intel.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Wed, Aug 23, 2017 at 12:03:39PM +0100, Ferruh Yigit wrote: > On 8/21/2017 8:47 AM, Sagi Grimberg wrote: > > From: Shahaf Shuler > > > > By default, Verbs maps the doorbell register to write combining. > > Working with write combining is useful for drivers which use blue flame > > for the doorbell write. > > > > Since mlx5 PMD uses only doorbells and write combining mapping requires > > an extra memory barrier to flush the doorbell after its write, setting > > the mapping to un-cached by default. > > > > Such change is reduces the max and average round trip > > latency significantly. > > > > Reported-by: Alexander Solganik > > Signed-off-by: Shahaf Shuler > > Signed-off-by: Yongseok Koh > > Signed-off-by: Alexander Solganik > > Signed-off-by: Sagi Grimberg > > --- > > drivers/net/mlx5/mlx5.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/net/mlx5/mlx5.c b/drivers/net/mlx5/mlx5.c > > index b7e5046325c0..4c2a0b9652e3 100644 > > --- a/drivers/net/mlx5/mlx5.c > > +++ b/drivers/net/mlx5/mlx5.c > > @@ -920,6 +920,8 @@ rte_mlx5_pmd_init(void) > > * using this PMD, which is not supported in forked processes. > > */ > > setenv("RDMAV_HUGEPAGES_SAFE", "1", 1); > > + /* Don't map UAR to WC if BlueFlame is not used.*/ > > + setenv("MLX5_SHUT_UP_BF", "1", 1); > > Although technically this is possible, I wonder how good idea it is a > driver communicating with other processes via system environment variable? We don't have such flexibility though verbs, those environment variable are read by libmlx5 code and the PMD is linked though libibverbs which does not provide a "clean" way tweak libmlx5. It is not used to communicate with another process, it is the same process executing the code which reads those environment variables. Currently it is the only solution we have. For the patch: Acked-by: Nelio Laranjeiro Thanks, -- Nélio Laranjeiro 6WIND