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([2a00:1098:3142:14:3110:d736:2a7:6aff]) by smtp.gmail.com with ESMTPSA id q4-20020adfbb84000000b0020c5253d90esm11838361wrg.90.2022.05.23.04.22.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 May 2022 04:22:18 -0700 (PDT) Message-ID: Date: Mon, 23 May 2022 12:22:18 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: vchiq: Performance regression since 5.18-rc1 To: Stefan Wahren , paulmck@kernel.org Cc: Marcelo Tosatti , Andrew Morton , Nicolas Saenz Julienne , Borislav Petkov , Minchan Kim , Mel Gorman , Juri Lelli , Thomas Gleixner , Sebastian Andrzej Siewior , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linux ARM , regressions@lists.linux.dev, riel@surriel.com, viro@zeniv.linux.org.uk References: <77d6d498-7dd9-03eb-60f2-d7e682bb1b20@i2se.com> <20220521234616.GO1790663@paulmck-ThinkPad-P17-Gen-1> <20220523044818.GS1790663@paulmck-ThinkPad-P17-Gen-1> <58cb7fbb-d317-83e6-0427-d3f3944b24b8@raspberrypi.com> <2ddd354e-a2b6-077c-25be-6ef1b2118d04@i2se.com> From: Phil Elwell In-Reply-To: <2ddd354e-a2b6-077c-25be-6ef1b2118d04@i2se.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/05/2022 12:15, Stefan Wahren wrote: > Hi Phil, > > Am 23.05.22 um 13:01 schrieb Phil Elwell: >> Hi Stefan, >> >> On 23/05/2022 11:48, Stefan Wahren wrote: >>> Hi Phil, >>> >>> Am 23.05.22 um 11:29 schrieb Phil Elwell: >>>> Hi Stefan, >>>> >>>> On 23/05/2022 07:19, Stefan Wahren wrote: >>>>> Hi Paul, >>>>> >>>>> Am 23.05.22 um 06:48 schrieb Paul E. McKenney: >>>>>> On Sun, May 22, 2022 at 05:11:36PM +0200, Stefan Wahren wrote: >>>>>>> Hi Paul, >>>>>>> >>>>>>> Am 22.05.22 um 01:46 schrieb Paul E. McKenney: >>>>>>>> On Sun, May 22, 2022 at 01:22:00AM +0200, Stefan Wahren wrote: >>>>>>>>> Hi, >>>>>>>>> >>>>>>>>> while testing the staging/vc04_services/interface/vchiq_arm driver with my >>>>>>>>> Raspberry Pi 3 B+ (multi_v7_defconfig) i noticed a huge performance >>>>>>>>> regression since [ff042f4a9b050895a42cae893cc01fa2ca81b95c] mm: >>>>>>>>> lru_cache_disable: replace work queue synchronization with synchronize_rcu >>>>>>>>> >>>>>>>>> Usually i run "vchiq_test -f 1" to see the driver is still working [1]. >>>>>>>>> >>>>>>>>> Before commit: >>>>>>>>> >>>>>>>>> real    0m1,500s >>>>>>>>> user    0m0,068s >>>>>>>>> sys    0m0,846s >>>>>>>>> >>>>>>>>> After commit: >>>>>>>>> >>>>>>>>> real    7m11,449s >>>>>>>>> user    0m2,049s >>>>>>>>> sys    0m0,023s >>>>>>>>> >>>>>>>>> Best regards >>>>>>>>> >>>>>>>>> [1] - https://github.com/raspberrypi/userland >>>>>>>> Please feel free to try the patch shown below.  Or the pair of patches >>>>>>>> from Rik here: >>>>>>>> >>>>>>>> https://lore.kernel.org/lkml/20220218183114.2867528-2-riel@surriel.com/ >>>>>>>> https://lore.kernel.org/lkml/20220218183114.2867528-3-riel@surriel.com/ >>>>>>> I tried your patch and Rik's patches but in both cases vchiq_test runs 7 >>>>>>> minutes instead of ~ 1 second. >>>>>> That is surprising.  Do you boot with rcupdate.rcu_normal=1? >>>>> No, not explicit. >>>>>>    That would >>>>>> nullify my patch, but I would expect that Rik's patch would still provide >>>>>> increased performance even in that case. >>>>> I will retest with a fresh SD card image. >>>>>> >>>>>> Could you please characterize where the slowdown is occurring? >>>>> >>>>> Unfortunately i don't have a deep insight into driver and vchiq_test tool. >>>>> Just a user view. >>>>> >>>>> Do you think an strace would be a good starting point? >>>>> >>>>> @Phil Any advices to analyse this issue? >>>> >>>> Sending many small control packets: >>>> >>>>    vchiq_test -c 1 10000 >>>> >>>> essentially tests interrupt latency. Using a small number of large bulk >>>> transfers: >>>> >>>>    vchiq_test -b 10000 1 >>>> >>>> becomes a test of how long it takes to lock down pages. It also tests DMA >>>> transfer speeds, but since the DMA is run by the firmware (which you aren't >>>> changing), I think you can rule that. >>> Thanks i will try. >>>> >>>> You may also find it helpful to include "force_turbo=1" in config.txt for >>>> more predictable results. >>>> >>>> By the way, running our 5.18-rc7-based branch on a 3B+ I'm not seeing any >>>> performance problems: >>> I assume you are using arm/bcm2709_defconfig and not arm/multi_v7_defconfig >>> as me? >> >> That's correct. Simply switching to multi_v7_defconfig breaks vchiq >> completely, presumably because it doesn't define CONFIG_BCM2835_VCHIQ. > sorry, forgot to mention. I that i enable VCHIQ as module on top of > multi_v7_defconfig. Downstream tree with multi_v7_defconfig + CONFIG_BCM2835_VCHIQ: pi@raspberrypi:~$ time vchiq_test -f 1 Functional test - iters:1 ======== iteration 1 ======== Testing bulk transfer for alignment. Testing bulk transfer at PAGE_SIZE. real 0m0.566s user 0m0.037s sys 0m0.166s Phil