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Date: Wed, 8 Oct 2014 13:59:11 +0200 From: Grozdan <neutrino8@...il.com> To: Austin S Hemmelgarn <ahferroin7@...il.com> Cc: linux-kernel@...r.kernel.org Subject: Re: High latency while CPU is under full load On Wed, Oct 8, 2014 at 1:44 PM, Austin S Hemmelgarn <ahferroin7@...il.com> wrote: > On 2014-10-07 15:28, Grozdan wrote: >> >> Hi, >> >> Basically, my problem is this: >> >> I'm doing a lot of audio/video encoding on an AMD FX8350. The encoder >> process always runs at nice 10. Even so, my whole system feels very >> sluggish. Switching between different app windows and/or virtual >> desktops takes up usually 3-5 seconds giving the impression that there >> is not enough processing power. Browsing the web is also severely >> impacted. >> >> I had to tune CFS in order to be (much) more responsive during an >> encoding session. This has worked out pretty well thus far, but it is >> my opinion that the user should *not* need to fiddle with buttons to >> make his system respond fluently even under high load. The below is >> what I had to do in order to get a snappy system during such load >> >> kernel.sched_nr_migrate = 64 >> kernel.sched_latency_ns = 65000000 >> kernel.sched_wakeup_granularity_ns = 100000 >> kernel.sched_min_granularity_ns = 100000 >> kernel.sched_migration_cost_ns = 7000000 >> >> I have tried 3 different kernels, including one compiled myself, but >> the results are the same >> Kernels I tried were: 3.11.10, 3.12 and 3.16.4 (self-compiled) >> >> My system specs are as follows >> >> CPU: AMD FX-8350 @ 4GHz >> RAM: 16GB DDR1333 >> GPU: NVIDIA GTX 560 with NV blob driver >> HDD: Seagate Constellation ES.3 128MB cache >> Desktop: KDE 4.11 >> > Are you using a kernel with CONFIG_PREEMPT=y? I've personally found that > that can help hugely with UI sluggishness (and also tends to get better > results when doing stuff like live video capture), although to get this you > may need to build the kernel yourself. Also, I would suggest trying the > deadline I/O scheduler; I've found it provides much better latency than CFQ > for most workloads, and you almost certainly don't need I/O priorities. > I've actually got a similar setup (FX-8320 @ 4GHz, 16GB DDR3-1600, High-end > storage, and a Radeon R7-240 GPU), and had similar issues when doing > processing of big (>500MB) images in GIMP, and using a CONFIG_PREEMPT > enabled kernel and the deadline I/O scheduler has pretty much resolved all > of these issues. > > Additionally, try with KDE's 'semantic desktop' functionality turned off, > this eats a huge amount of disk and memory bandwidth, and can easily bring a > system to it's knees. Furthermore, unless you can reproduce things using > nouevau instead of the NV driver, you're not as likely to get a lot of help. > > Hi, Yes, PREEMP is enabled and the I/O scheduler used is BFQ. But the problem existed regardless of the I/O scheduler I've followed the suggestions of Mike and set the CFS values a little bit lower than their standard ones and it appears to have improved. There is sometimes a very small delay while opening something, but I guess this is from the heavy load. I also turned off the KDE effects and it's much more snappy now but I turned a few back on as I like the animations of opening/closing windows :P I have not tested the nouveau driver as I need VDPAU here. Also updated the NV blob to latest version and it seems to improve a bit. In the changelog it was mentioned that there was a fix "Fixed an OpenGL issue that could cause glReadPixels() operations to be improperly clipped when resizing composited application windows, potentially leading to momentary X freezes." I do not have KDE's semantic stuff enabled here as it's useless for me This is the vmstat output. I have no idea what it means procs -----------memory---------- ---swap-- -----io---- -system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 10 0 0 10298064 428 2873036 0 0 648 542 144 140 90 1 8 1 0 11 0 0 10295352 428 2874160 0 0 1024 0 9498 6792 88 1 12 0 0 10 0 0 10290824 428 2879140 0 0 3212 1540 9366 6305 89 1 10 0 0 10 0 0 10288868 428 2880944 0 0 896 0 8826 6037 89 1 10 0 0 9 0 0 10286796 428 2883188 0 0 1920 172 8635 5447 89 1 10 0 0 12 0 0 10284848 428 2885508 0 0 896 1684 9162 6119 88 1 11 0 0 11 0 0 10280436 428 2888896 0 0 2560 0 8702 6206 86 2 12 0 0 12 0 0 10279448 428 2889744 0 0 640 0 8757 5915 91 1 8 0 0 10 0 0 10276564 428 2892480 0 0 1920 4168 8649 5471 88 1 11 0 0 -- Yours truly -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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