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Message-ID: <47A21DC0.7030202@qualcomm.com> Date: Thu, 31 Jan 2008 11:13:04 -0800 From: Max Krasnyanskiy <maxk@...lcomm.com> To: Mark Hounschell <dmarkh@....rr.com> CC: linux-kernel@...r.kernel.org Subject: Re: [CPUISOL] CPU isolation extensions Hi Mark, > maxk@...lcomm.com wrote: >> Following patch series extends CPU isolation support. Yes, most people want to virtuallize >> CPUs these days and I want to isolate them :). >> The primary idea here is to be able to use some CPU cores as dedicated engines for running >> user-space code with minimal kernel overhead/intervention, think of it as an SPE in the >> Cell processor. >> >> We've had scheduler support for CPU isolation ever since O(1) scheduler went it. >> I'd like to extend it further to avoid kernel activity on those CPUs as much as possible. >> In fact that the primary distinction that I'm making between say "CPU sets" and >> "CPU isolation". "CPU sets" let you manage user-space load while "CPU isolation" provides >> a way to isolate a CPU as much as possible (including kernel activities). >> >> I'm personally using this for hard realtime purposes. With CPU isolation it's very easy to >> achieve single digit usec worst case and around 200 nsec average response times on off-the-shelf >> multi- processor/core systems under exteme system load. I'm working with legal folks on releasing >> hard RT user-space framework for that. >> I can also see other application like simulators and stuff that can benefit from this. >> >> I've been maintaining this stuff since around 2.6.18 and it's been running in production >> environment for a couple of years now. It's been tested on all kinds of machines, from NUMA >> boxes like HP xw9300/9400 to tiny uTCA boards like Mercury AXA110. >> The messiest part used to be SLAB garbage collector changes. With the new SLUB all that mess >> goes away (ie no changes necessary). Also CFS seems to handle CPU hotplug much better than O(1) >> did (ie domains are recomputed dynamically) so that isolation can be done at any time (via sysfs). >> So this seems like a good time to merge. >> >> Anyway. The patchset consist of 5 patches. First three are very simple and non-controversial. >> They simply make "CPU isolation" a configurable feature, export cpu_isolated_map and provide >> some helper functions to access it (just like cpu_online() and friends). >> Last two patches add support for isolating CPUs from running workqueus and stop machine. >> More details in the individual patch descriptions. >> >> Ideally I'd like all of this to go in during this merge window. If people think it's acceptable >> Linus or Andrew (or whoever is more appropriate Ingo maybe) can pull this patch set from >> git://git.kernel.org/pub/scm/linux/kernel/git/maxk/cpuisol-2.6.git >> > > It's good to see hear from someone else that thinks a multi-processor > box _should_ be able to run a CPU intensive (%100) RT app on one of the > processors without adversely affecting or being affected by the others. > I have had issues that were _traced_ back to the fact that I am doing > just that. All I got was, you can't do that or we don't support that > kind of thing in the Linux kernel. > > One example, Andrew Mortons feedback to the LKML thread "floppy.c soft lockup" > > Good luck with this. I hope this gets someones attention. Thanks for the support. I do the best I can because just like you I believe that it's a perfectly valid workload and there a lot of interesting applications that will benefit from mainline support. > BTW, I have tried your patches against a vanilla 2.6.24 kernel but am > not successful. > > # echo '1' > /sys/devices/system/cpu/cpu1/isolated > bash: echo: write error: Device or resource busy You have to bring it offline first. In other words: echo 0 > /sys/devices/system/cpu/cpu1/online echo 1 > /sys/devices/system/cpu/cpu1/isolated echo 1 > /sys/devices/system/cpu/cpu1/online > The cpuisol=1 cmdline option yields: > > harley:# cat /sys/devices/system/cpu/cpu1/isolated > 0 > > harley:# cat /proc/cmdline > root=/dev/sda3 vga=normal apm=off selinux=0 noresume splash=silent > kmalloc=192M cpuisol=1 Sorry my bad. I had a typo in the patch description the option is "isolcpus=N". We've had that option for awhile now. I mean it's not even part of my patch. Thanx Max -- 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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