From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id BD73DA00C3; Mon, 17 Jan 2022 18:35:13 +0100 (CET) Received: from [217.70.189.124] (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 760974122E; Mon, 17 Jan 2022 18:35:13 +0100 (CET) Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by mails.dpdk.org (Postfix) with ESMTP id A739040143 for ; Mon, 17 Jan 2022 18:35:11 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1642440912; x=1673976912; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=aycNyHyYSGR+Bq1zY4OQRt61ERoUC/lPIL0LpUV/og8=; b=acpkkIZ8g3a4Bmgx6aG/oQSwxSY+5nhEc2SYuWSLkGDOEHpECt8bbp0F tWB9U3ugHS5gqyFYcgbhTyCOZ7IbIbVr6joZmKdpzSRBRLUT1cR/9CvX4 NgwnTqhJxeE6yoRrMqMi5mRvYyp6LpcoxnTbXKSz3DccMgDqQQHldlWB7 di1VAoi1ckYqHtqbwZBxZHIznVtS4OB7nEASCp1IpbG3g/ZadKBquSPA7 zZRX00HIxFTq/q+RrumxMmLxmTeOm+SEuZM2JOXeddreR4jwHEOUKfUaG op2CPVCz0T4ReS+SC0eIymkJeYOwtyrIbMb8BNkZQYoDEh/gnOSMxLiVa g==; X-IronPort-AV: E=McAfee;i="6200,9189,10229"; a="331017609" X-IronPort-AV: E=Sophos;i="5.88,296,1635231600"; d="scan'208";a="331017609" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jan 2022 09:35:10 -0800 X-IronPort-AV: E=Sophos;i="5.88,296,1635231600"; d="scan'208";a="531421766" Received: from bricha3-mobl.ger.corp.intel.com ([10.252.26.87]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-SHA; 17 Jan 2022 09:35:08 -0800 Date: Mon, 17 Jan 2022 17:35:05 +0000 From: Bruce Richardson To: Morten =?iso-8859-1?Q?Br=F8rup?= Cc: olivier.matz@6wind.com, andrew.rybchenko@oktetlabs.ru, jerinjacobk@gmail.com, dev@dpdk.org Subject: Re: [PATCH] mempool: fix get objects from mempool with cache Message-ID: References: <98CBD80474FA8B44BF855DF32C47DC35D86DB2@smartserver.smartshare.dk> <20220114163650.94288-1-mb@smartsharesystems.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220114163650.94288-1-mb@smartsharesystems.com> X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org On Fri, Jan 14, 2022 at 05:36:50PM +0100, Morten Brørup wrote: > A flush threshold for the mempool cache was introduced in DPDK version > 1.3, but rte_mempool_do_generic_get() was not completely updated back > then, and some inefficiencies were introduced. > > This patch fixes the following in rte_mempool_do_generic_get(): > > 1. The code that initially screens the cache request was not updated > with the change in DPDK version 1.3. > The initial screening compared the request length to the cache size, > which was correct before, but became irrelevant with the introduction of > the flush threshold. E.g. the cache can hold up to flushthresh objects, > which is more than its size, so some requests were not served from the > cache, even though they could be. > The initial screening has now been corrected to match the initial > screening in rte_mempool_do_generic_put(), which verifies that a cache > is present, and that the length of the request does not overflow the > memory allocated for the cache. > > 2. The function is a helper for rte_mempool_generic_get(), so it must > behave according to the description of that function. > Specifically, objects must first be returned from the cache, > subsequently from the ring. > After the change in DPDK version 1.3, this was not the behavior when > the request was partially satisfied from the cache; instead, the objects > from the ring were returned ahead of the objects from the cache. This is > bad for CPUs with a small L1 cache, which benefit from having the hot > objects first in the returned array. (This is also the reason why > the function returns the objects in reverse order.) > Now, all code paths first return objects from the cache, subsequently > from the ring. > > 3. If the cache could not be backfilled, the function would attempt > to get all the requested objects from the ring (instead of only the > number of requested objects minus the objects available in the ring), > and the function would fail if that failed. > Now, the first part of the request is always satisfied from the cache, > and if the subsequent backfilling of the cache from the ring fails, only > the remaining requested objects are retrieved from the ring. > > 4. The code flow for satisfying the request from the cache was slightly > inefficient: > The likely code path where the objects are simply served from the cache > was treated as unlikely. Now it is treated as likely. > And in the code path where the cache was backfilled first, numbers were > added and subtracted from the cache length; now this code path simply > sets the cache length to its final value. > > 5. Some comments were not correct anymore. > The comments have been updated. > Most importanly, the description of the succesful return value was > inaccurate. Success only returns 0, not >= 0. > > Signed-off-by: Morten Brørup > --- I am a little uncertain about the reversing of the copies taking things out of the mempool - for machines where we are not that cache constrainted will we lose out in possible optimizations where the compiler optimizes the copy loop as a memcpy? Otherwise the logic all looks correct to me. /Bruce