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[204.195.112.199]) by smtp.gmail.com with ESMTPSA id e21-20020a170902d39500b0015e8d4eb2aesm1943566pld.248.2022.05.06.09.33.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 May 2022 09:33:44 -0700 (PDT) Date: Fri, 6 May 2022 09:33:41 -0700 From: Stephen Hemminger To: Bruce Richardson Cc: Honnappa Nagarahalli , Tyler Retzlaff , "dev@dpdk.org" , nd , "Ananyev, Konstantin" Subject: Re: [RFC] rte_ring: don't use always inline Message-ID: <20220506093341.785086a7@hermes.local> In-Reply-To: References: <20220505224547.394253-1-stephen@networkplumber.org> <20220506072434.GA19777@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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, 6 May 2022 16:28:41 +0100 Bruce Richardson wrote: > On Fri, May 06, 2022 at 03:12:32PM +0000, Honnappa Nagarahalli wrote: > > > > > > > > On Thu, May 05, 2022 at 10:59:32PM +0000, Honnappa Nagarahalli wrote: > > > > Thanks Stephen. Do you see any performance difference with this change? > > > > > > as a matter of due diligence i think a comparison should be made just to be > > > confident nothing is regressing. > > > > > > i support this change in principal since it is generally accepted best practice to > > > not force inlining since it can remove more valuable optimizations that the > > > compiler may make that the human can't see. > > > the optimizations may vary depending on compiler implementation. > > > > > > force inlining should be used as a targeted measure rather than blanket on > > > every function and when in use probably needs to be periodically reviewed and > > > potentially removed as the code / compiler evolves. > > > > > > also one other consideration is the impact of a particular compiler's force > > > inlining intrinsic/builtin is that it may permit inlining of functions when not > > > declared in a header. i.e. a function from one library may be able to be inlined > > > to another binary as a link time optimization. although everything here is in a > > > header so it's a bit moot. > > > > > > i'd like to see this change go in if possible. > > Like Stephen mentions below, I am sure we will have a for and against discussion here. > > As a DPDK community we have put performance front and center, I would prefer to go down that route first. > > > > I ran some initial numbers with this patch, and the very quick summary of > what I've seen so far: > > * Unit tests show no major differences, and while it depends on what > specific number you are interested in, most seem within margin of error. > * Within unit tests, the one number I mostly look at when considering > inlining is the "empty poll" cost, since I believe we should look to keep > that as close to zero as possible. In the past I've seen that number jump > from 3 cycles to 12 cycles due to missed inlining. In this case, it seem > fine. > * Ran a quick test with the eventdev_pipeline example app using SW eventdev, > as a test of an actual app which is fairly ring-heavy [used 8 workers > with 1000 cycles per packet hop]. (Thanks to Harry vH for this suggestion > of a workload) > * GCC 8 build - no difference observed > * GCC 11 build - approx 2% perf reduction observed > > As I said, these are just some quick rough numbers, and I'll try and get > some more numbers on a couple of different platforms, see if the small > reduction seen is consistent or not. I may also test a few differnet > combinations/options in the eventdev test. It would be good if others also > tested on a few platforms available to them. > > /Bruce I wonder if a mixed approach might help where some key bits were marked as more important to inline? Or setting compiler flags in build infra?