On Tue, 1 Nov 2005, Dave Hansen wrote:
> On Tue, 2005-11-01 at 07:25 -0800, Martin J. Bligh wrote:
> > > I really don't think we *want* to say we support higher order allocations
> > > absolutely robustly, nor do we want people using them if possible. Because
> > > we don't. Even with your patches.
> > >
> > > Ingo also brought up this point at Ottawa.
> >
> > Some of the driver issues can be fixed by scatter-gather DMA *if* the
> > h/w supports it. But what exactly do you propose to do about kernel
> > stacks, etc? By the time you've fixed all the individual usages of it,
> > frankly, it would be easier to provide a generic mechanism to fix the
> > problem ...
>
> That generic mechanism is the kernel virtual remapping. However, it has
> a runtime performance cost, which is increased TLB footprint inside the
> kernel, and a more costly implementation of __pa() and __va().
>
> I'll admit, I'm biased toward partial solutions without runtime cost
> before we start incurring constant cost across the entire kernel,
> especially when those partial solutions have other potential in-kernel
> users.
To give an idea of the increased TLB footprint, I ran an aim9 test with
cpu_has_pse disabled in include/arch-i386/cpufeature.h to force the use
of small pages for the physical memory mappings.
This is the -clean results
clean clean-nopse
1 creat-clo 16006.00 15294.90 -711.10 -4.44% File Creations and Closes/second
2 page_test 117515.83 118677.11 1161.28 0.99% System Allocations & Pages/second
3 brk_test 440289.81 436042.64 -4247.17 -0.96% System Memory Allocations/second
4 jmp_test 4179466.67 4173266.67 -6200.00 -0.15% Non-local gotos/second
5 signal_test 80803.20 78286.95 -2516.25 -3.11% Signal Traps/second
6 exec_test 61.75 60.45 -1.30 -2.11% Program Loads/second
7 fork_test 1327.01 1318.11 -8.90 -0.67% Task Creations/second
8 link_test 5531.53 5406.60 -124.93 -2.26% Link/Unlink Pairs/second
This is what mbuddy-v19 with and without pse looks like
mbuddy-v19 mbuddy-v19-nopse
1 creat-clo 15889.41 15328.22 -561.19 -3.53% File Creations and Closes/second
2 page_test 117082.15 116892.70 -189.45 -0.16% System Allocations & Pages/second
3 brk_test 437887.37 432716.97 -5170.40 -1.18% System Memory Allocations/second
4 jmp_test 4179950.00 4176087.32 -3862.68 -0.09% Non-local gotos/second
5 signal_test 85335.78 78553.57 -6782.21 -7.95% Signal Traps/second
6 exec_test 61.92 60.61 -1.31 -2.12% Program Loads/second
7 fork_test 1342.21 1292.26 -49.95 -3.72% Task Creations/second
8 link_test 5555.55 5412.90 -142.65 -2.57% Link/Unlink Pairs/second
--
Mel Gorman
Part-time Phd Student Java Applications Developer
University of Limerick IBM Dublin Software Lab
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