On Tuesday, July 25, 2017 10:56:15 AM Bartlomiej Zolnierkiewicz wrote: > On Tuesday, July 25, 2017 02:00:00 PM Dave Airlie wrote: > > On 19 July 2017 at 00:34, Peter Jones <pjones@xxxxxxxxxx> wrote: > > > On Tue, Jul 18, 2017 at 04:09:09PM +1000, Dave Airlie wrote: > > >> This patch allows the user to disable write combined mapping > > >> of the efifb framebuffer console using an nowc option. > > >> > > >> A customer noticed major slowdowns while logging to the console > > >> with write combining enabled, on other tasks running on the same > > >> CPU. (10x or greater slow down on all other cores on the same CPU > > >> as is doing the logging). > > >> > > >> I reproduced this on a machine with dual CPUs. > > >> Intel(R) Xeon(R) CPU E5-2609 v3 @ 1.90GHz (6 core) > > >> > > >> I wrote a test that just mmaps the pci bar and writes to it in > > >> a loop, while this was running in the background one a single > > >> core with (taskset -c 1), building a kernel up to init/version.o > > >> (taskset -c 8) went from 13s to 133s or so. I've yet to explain > > >> why this occurs or what is going wrong I haven't managed to find > > >> a perf command that in any way gives insight into this. > > >> > > >> 11,885,070,715 instructions # 1.39 insns per cycle > > >> vs > > >> 12,082,592,342 instructions # 0.13 insns per cycle > > >> > > >> is the only thing I've spotted of interest, I've tried at least: > > >> dTLB-stores,dTLB-store-misses,L1-dcache-stores,LLC-store,LLC-store-misses,LLC-load-misses,LLC-loads,\mem-loads,mem-stores,iTLB-loads,iTLB-load-misses,cache-references,cache-misses > > >> > > >> For now it seems at least a good idea to allow a user to disable write > > >> combining if they see this until we can figure it out. > > > > > > Well, that's kind of amazing, given 3c004b4f7eab239e switched us /to/ > > > using ioremap_wc() for the exact same reason. I'm not against letting > > > the user force one way or the other if it helps, though it sure would be > > > nice to know why. > > > > > > Anyway, > > > > > > Acked-By: Peter Jones <pjones@xxxxxxxxxx> > > > > > > Bartlomiej, do you want to handle this in your devel tree? > > > > I'm happy to stick this in a drm-fixes pull with this ack. > > I'll put it into fbdev fixes for 4.13 with other fbdev patches. Patch queued for 4.13, thanks. Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
