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Miller" , Paolo Abeni , Maxime Coquelin , Rayagond Kokatanur , netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Voon Wei Feng , Wong Vee Khee , Song Yoong Siang , Alexandre Torgue Subject: Re: [PATCH net 1/1] net: stmmac: add fsleep() in HW Rx timestamp checking loop Message-ID: <20220419005220.GA17634@linux.intel.com> References: <20220413040115.2351987-1-tee.min.tan@intel.com> <20220413125915.GA667752@hoboy.vegasvil.org> <20220414072934.GA10025@linux.intel.com> <20220414104259.0b928249@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220414104259.0b928249@kernel.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220418_175429_471327_26784ACA X-CRM114-Status: GOOD ( 24.74 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; 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X-IronPort-AV: E=McAfee;i="6400,9594,10321"; a="324085422" X-IronPort-AV: E=Sophos;i="5.90,271,1643702400"; d="scan'208";a="324085422" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2022 17:54:23 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.90,271,1643702400"; d="scan'208";a="554472469" Received: from linux.intel.com ([10.54.29.200]) by orsmga007.jf.intel.com with ESMTP; 18 Apr 2022 17:54:23 -0700 Received: from linux.intel.com (ssid-ilbpg3-teeminta.png.intel.com [10.88.227.74]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by linux.intel.com (Postfix) with ESMTPS id 66F865808AE; Mon, 18 Apr 2022 17:54:19 -0700 (PDT) Date: Tue, 19 Apr 2022 08:52:20 +0800 From: Tan Tee Min To: Jakub Kicinski Cc: Richard Cochran , Tan Tee Min , Giuseppe Cavallaro , Alexandre Torgue , Jose Abreu , "David S . Miller" , Paolo Abeni , Maxime Coquelin , Rayagond Kokatanur , netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Voon Wei Feng , Wong Vee Khee , Song Yoong Siang , Alexandre Torgue Subject: Re: [PATCH net 1/1] net: stmmac: add fsleep() in HW Rx timestamp checking loop Message-ID: <20220419005220.GA17634@linux.intel.com> References: <20220413040115.2351987-1-tee.min.tan@intel.com> <20220413125915.GA667752@hoboy.vegasvil.org> <20220414072934.GA10025@linux.intel.com> <20220414104259.0b928249@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220414104259.0b928249@kernel.org> User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 14, 2022 at 10:42:59AM +0200, Jakub Kicinski wrote: > On Thu, 14 Apr 2022 15:29:34 +0800 Tan Tee Min wrote: > > > > --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c > > > > +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c > > > > @@ -279,10 +279,11 @@ static int dwmac4_wrback_get_rx_timestamp_status(void *desc, void *next_desc, > > > > /* Check if timestamp is OK from context descriptor */ > > > > do { > > > > ret = dwmac4_rx_check_timestamp(next_desc); > > > > - if (ret < 0) > > > > + if (ret <= 0) > > > > goto exit; > > > > i++; > > > > > > > > + fsleep(1); > > > > > > This is nutty. Why isn't this code using proper deferral mechanisms > > > like work or kthread? > > > > Appreciate your comment. > > The dwmac4_wrback_get_rx_timestamp_status() is called by stmmac_rx() > > function which is scheduled by NAPI framework. > > Do we still need to create deferred work inside NAPI work? > > Would you mind to explain it more in detail? > > fsleep() is a big hammer, can you try cpu_relax() and bumping the max > loop count a little? Thanks for the suggestion! I tried cpu_relax(), unfortunately the issue still happens when the system is in a high-load situation. I agree that the fsleep(1) (=1us) is a big hammer. Thus in order to improve this, I’ve figured out a smaller delay time that is enough for the context descriptor to be ready which is ndelay(500) (=500ns). Would you think this is more acceptable?