Messages in this thread | | | From | Ozgur <> | Subject | Re: niced tasks on SMT system | Date | Thu, 28 Dec 2017 21:58:32 +0300 |
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28.12.2017, 21:54, "Pavel Machek" <pavel@ucw.cz>: > Hi! > >> > Ok, so I'm compiling, and I'd like to run a flight simulator. >> > >> > Flightgear normally does 20fps on my system... kinda low but playable. >> > >> > I have reniced make -j 5 fo kernel running. Scheduler gives 100% of >> > one of CPUs to Flightgear (good), but the smt sibling is used by the >> > compilation, and I'm down to 9 fps. Not good. >> > >> > Even with single-threaded make, I have 10-13fps. >> > >> > Is there way to learn which CPUs are SMT siblings? >> >> cat /sys/devices/system/cpu/cpu{N}/topology/thread_siblings > > Thanks for a hint. > > Well, something is definitely wrong there: > > pavel@duo:/data/l/linux-n900$ cat > /sys/devices/system/cpu/cpu0/topology/thread_siblings > 03
Ops,
do you fly on N900 via flightgear? :) I have two N900 and one run gentoo.
> I believe that means that cpu0 & cpu1 are sharing physical cpu. Yet, > when I run flightgear and "nice while1". flightgear goes to CPU#0 and > while1 to CPU#1. Would not it be nice if while1 went preferably to > CPUs #2 and #3? Ok. after a while while1 moved to cpu#2, good. > >> > Is there way to disable SMT during runtime? >> >> You could offline them, but wouldn't it be better to tell each which >> CPUs they can use, or perhaps partition your box with cpusets? > > Let me try offlining first... and yes, SMT seems to be problem here. > > | CPU0 | CPU1 | CPU2 | CPU3 | | > | flightgear | off | off | off | 21 fps | > | flightgear | while1 | off | off | 17 fps | > | flightgear+while1 | off | off | off | 10 fps | > | flightgear | off | while1 | off | 21 fps | > >> > Can I do something to improve Flightgear performance and still do >> > compilation? >> >> Sure, run everything associated with your game as RT, and everything >> not game gets the leftover cycles. If there are none, box will >> throttle RT to save itself from it's psycho :) driver and you'll know >> that you need a bigger box. (it's likely your phone) > >> Oh yeah, echo NO_RT_RUNTIME_SHARE > /sys/kernel/debug/sched_features >> before you try that, otherwise the throttle won't help. > > Sure, but that is not a problem I have. > > Scheduler already (correctly) decides that the game is important, and > gives game all the time it wants (100% of one CPU). That is not a problem. > > Problem seems to be that it schedules other tasks to SMT sibling, and > that slows down the game quite significantly. > > Best regards, > > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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