From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754964AbdEEGCG (ORCPT ); Fri, 5 May 2017 02:02:06 -0400 Received: from mail-wr0-f195.google.com ([209.85.128.195]:33353 "EHLO mail-wr0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751101AbdEEGCE (ORCPT ); Fri, 5 May 2017 02:02:04 -0400 From: Karim Eshapa To: oss@buserror.net Cc: claudiu.manoil@nxp.com, roy.pledge@nxp.com, colin.king@canonical.com, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Karim Eshapa Subject: RE: [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck hacking jiffies. Date: Fri, 5 May 2017 08:01:54 +0200 Message-Id: <1493964114-11296-1-git-send-email-karim.eshapa@gmail.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1493873917-7484-1-git-send-email-karim.eshapa@gmail.com> References: <1493873917-7484-1-git-send-email-karim.eshapa@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >On 5/4/2017 5:07 PM, Scott Wood wrote: >> On Thu, 2017-05-04 at 06:58 +0200, Karim Eshapa wrote: >>> + stop = jiffies + 10000; >>> + /* >>> + * if MR was full and h/w had other FQRNI entries to produce, we >>> + * need to allow it time to produce those entries once the >>> + * existing entries are consumed. A worst-case situation >>> + * (fully-loaded system) means h/w sequencers may have to do 3-4 >>> + * other things before servicing the portal's MR pump, each of >>> + * which (if slow) may take ~50 qman cycles (which is ~200 >>> + * processor cycles). So rounding up and then multiplying this >>> + * worst-case estimate by a factor of 10, just to be >>> + * ultra-paranoid, goes as high as 10,000 cycles. NB, we consume >>> + * one entry at a time, so h/w has an opportunity to produce new >>> + * entries well before the ring has been fully consumed, so >>> + * we're being *really* paranoid here. >>> + */ >> OK, upon reading this more closely it seems the intent was to delay for 10,000 >> *processor cycles* and somehow that got turned into 10,000 jiffies (which is >> 40 seconds at the default Hz!). We could just replace this whole thing with >> msleep(1) and still be far more paranoid than was originally intended. >> >> Claudiu and Roy, any comments? >Yes the timing here is certainly off, the code changed a few times since >the comment was originally written. >An msleep(1) seems reasonable here to me. If the previous patch with msleep(1) is OK. can I send a patch to slightly change the comments. Thanks, Karim